diff --git a/lib/clang/llvm.build.mk b/lib/clang/llvm.build.mk
index c731deba8976..e88b2ff1033e 100644
--- a/lib/clang/llvm.build.mk
+++ b/lib/clang/llvm.build.mk
@@ -1,132 +1,133 @@
 
 .include <src.opts.mk>
 
 .ifndef LLVM_BASE
 .error Please define LLVM_BASE before including this file
 .endif
 
 .ifndef LLVM_SRCS
 .error Please define LLVM_SRCS before including this file
 .endif
 
 .ifndef SRCDIR
 .error Please define SRCDIR before including this file
 .endif
 
 .ifndef OS_REVISION
 .error Please define OS_REVISION before including this file
 .endif
 
 .PATH:		${LLVM_BASE}/${SRCDIR}
 
 CFLAGS+=	-I${SRCTOP}/lib/clang/include
 CFLAGS+=	-I${LLVM_SRCS}/include
 CFLAGS+=	-D__STDC_CONSTANT_MACROS
 CFLAGS+=	-D__STDC_FORMAT_MACROS
 CFLAGS+=	-D__STDC_LIMIT_MACROS
 CFLAGS+=	-DHAVE_VCS_VERSION_INC
 .if ${MK_LLVM_ASSERTIONS} == "no"
 CFLAGS+=	-DNDEBUG
 .endif
 
 # Note that using TARGET_ARCH here is essential for a functional native-xtools
 # build!  For native-xtools, we're building binaries that will work on the
 # *host* machine (MACHINE_ARCH), but they should default to producing binaries
 # for the *target* machine (TARGET_ARCH).
 TARGET_ARCH?=	${MACHINE_ARCH}
 BUILD_ARCH?=	${MACHINE_ARCH}
 
 # Armv6 and armv7 uses hard float abi, unless the CPUTYPE has soft in it.
 # For all other targets, we stick with 'unknown'.
 .if ${TARGET_ARCH:Marm*}
 .if !defined(CPUTYPE) || ${CPUTYPE:M*soft*} == ""
 TARGET_TRIPLE_ABI=-gnueabihf
 .else
 TARGET_TRIPLE_ABI=-gnueabi
 .endif
 .else
 TARGET_TRIPLE_ABI=
 .endif
 VENDOR=		unknown
 
 LLVM_TARGET_TRIPLE?=	${TARGET_ARCH:C/amd64/x86_64/}-${VENDOR}-freebsd${OS_REVISION}${TARGET_TRIPLE_ABI}
 LLVM_BUILD_TRIPLE?=	${BUILD_ARCH:C/amd64/x86_64/}-${VENDOR}-freebsd${OS_REVISION}
 
 CFLAGS+=	-DLLVM_DEFAULT_TARGET_TRIPLE=\"${LLVM_TARGET_TRIPLE}\"
 CFLAGS+=	-DLLVM_HOST_TRIPLE=\"${LLVM_BUILD_TRIPLE}\"
 CFLAGS+=	-DDEFAULT_SYSROOT=\"${TOOLS_PREFIX}\"
 
 .if ${MK_LLVM_TARGET_AARCH64} != "no"
 CFLAGS+=	-DLLVM_TARGET_ENABLE_AARCH64
 . if ${MACHINE_CPUARCH} == "aarch64"
 LLVM_NATIVE_ARCH=	AArch64
 . endif
 .endif
 .if ${MK_LLVM_TARGET_ARM} != "no"
 CFLAGS+=	-DLLVM_TARGET_ENABLE_ARM
 . if ${MACHINE_CPUARCH} == "arm"
 LLVM_NATIVE_ARCH=	ARM
 . endif
 .endif
 .if ${MK_LLVM_TARGET_BPF} != "no"
 CFLAGS+=	-DLLVM_TARGET_ENABLE_BPF
 .endif
 .if ${MK_LLVM_TARGET_MIPS} != "no"
 CFLAGS+=	-DLLVM_TARGET_ENABLE_MIPS
 .endif
 .if ${MK_LLVM_TARGET_POWERPC} != "no"
 CFLAGS+=	-DLLVM_TARGET_ENABLE_POWERPC
 . if ${MACHINE_CPUARCH} == "powerpc"
 LLVM_NATIVE_ARCH=	PowerPC
 . endif
 .endif
 .if ${MK_LLVM_TARGET_RISCV} != "no"
 CFLAGS+=	-DLLVM_TARGET_ENABLE_RISCV
 . if ${MACHINE_CPUARCH} == "riscv"
 LLVM_NATIVE_ARCH=	RISCV
 . endif
 .endif
 .if ${MK_LLVM_TARGET_X86} != "no"
 CFLAGS+=	-DLLVM_TARGET_ENABLE_X86
 . if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"
 LLVM_NATIVE_ARCH=	X86
 . endif
 .endif
 
 .ifdef LLVM_NATIVE_ARCH
 CFLAGS+=	-DLLVM_NATIVE_ASMPARSER=LLVMInitialize${LLVM_NATIVE_ARCH}AsmParser
 CFLAGS+=	-DLLVM_NATIVE_ASMPRINTER=LLVMInitialize${LLVM_NATIVE_ARCH}AsmPrinter
 CFLAGS+=	-DLLVM_NATIVE_DISASSEMBLER=LLVMInitialize${LLVM_NATIVE_ARCH}Disassembler
 CFLAGS+=	-DLLVM_NATIVE_TARGET=LLVMInitialize${LLVM_NATIVE_ARCH}Target
 CFLAGS+=	-DLLVM_NATIVE_TARGETINFO=LLVMInitialize${LLVM_NATIVE_ARCH}TargetInfo
 CFLAGS+=	-DLLVM_NATIVE_TARGETMC=LLVMInitialize${LLVM_NATIVE_ARCH}TargetMC
 .endif
 
 CFLAGS+=	-ffunction-sections
 CFLAGS+=	-fdata-sections
 .include "bsd.linker.mk"
 .if ${LINKER_TYPE} == "mac"
 LDFLAGS+=	-Wl,-dead_strip
 .else
 LDFLAGS+=	-Wl,--gc-sections
 # XXX: --gc-sections strips the ELF brand note and on RISC-V the OS/ABI ends up
 # as NONE, so for statically-linked binaries, i.e. lacking an interpreter,
 # get_brandinfo finds nothing and (f)execve fails with ENOEXEC. Work around
 # this by manually setting the OS/ABI field via the emulation.
 .if ${MACHINE_ARCH:Mriscv64*} != "" && ${NO_SHARED:Uno:tl} != "no" && \
     (${.MAKE.OS} == "FreeBSD" || !defined(BOOTSTRAPPING))
 LDFLAGS+=	-Wl,-m,elf64lriscv_fbsd
 .endif
 .endif
 
+CXXSTD=		c++17
 CXXFLAGS+=	-fno-exceptions
 CXXFLAGS+=	-fno-rtti
 .if ${.MAKE.OS} == "FreeBSD" || !defined(BOOTSTRAPPING)
 CXXFLAGS.clang+= -stdlib=libc++
 .else
 # Building on macOS/Linux needs the real sysctl() not the bootstrap tools stub.
 CFLAGS+=	-DBOOTSTRAPPING_WANT_NATIVE_SYSCTL
 .endif
 .if defined(BOOTSTRAPPING) && ${.MAKE.OS} == "Linux"
 LIBADD+=	dl
 .endif
diff --git a/lib/libclang_rt/Makefile.inc b/lib/libclang_rt/Makefile.inc
index e7db5a469661..c472e8b741be 100644
--- a/lib/libclang_rt/Makefile.inc
+++ b/lib/libclang_rt/Makefile.inc
@@ -1,35 +1,36 @@
 .include <bsd.compiler.mk>
 
 PACKAGE=	clang
 CRTSRC=		${SRCTOP}/contrib/llvm-project/compiler-rt
 .include "compiler-rt-vars.mk"
 
 .PATH:		${CRTSRC}/lib
 
 LIBDIR=		${SANITIZER_LIBDIR}
 SHLIBDIR=	${LIBDIR}
 
 NO_PIC=
 MK_ASAN:=	no
 MK_SSP=		no
 MK_UBSAN:=	no
 
 WARNS?=		0
 
 CFLAGS+=	-DNDEBUG
 CFLAGS+=	-DHAVE_RPC_XDR_H=0
 CFLAGS+=	-DSANITIZER_SUPPORTS_WEAK_HOOKS=0
 CFLAGS+=	-DUBSAN_CAN_USE_CXXABI
 CFLAGS+=	${PICFLAG}
 CFLAGS+=	-fno-builtin
 CFLAGS+=	-fno-exceptions
 CXXFLAGS+=	-fno-rtti
 .if ${COMPILER_TYPE} == clang
 CFLAGS+=	-fno-sanitize=safe-stack
 .endif
 CFLAGS+=	-fno-stack-protector
 CFLAGS+=	-funwind-tables
 CXXFLAGS+=	-fvisibility-inlines-hidden
 CXXFLAGS+=	-fvisibility=hidden
 CFLAGS+=	-I${CRTSRC}/include
 CFLAGS+=	-I${CRTSRC}/lib
+CXXSTD=		c++17
diff --git a/lib/libomp/Makefile b/lib/libomp/Makefile
index f1513e70f3f6..6c14c7d21077 100644
--- a/lib/libomp/Makefile
+++ b/lib/libomp/Makefile
@@ -1,96 +1,97 @@
 # z_Linux_asm.S is missing BTI support
 MK_BRANCH_PROTECTION=no
 
 .include <bsd.compiler.mk>
 
 SHLIB_NAME=	libomp.so
 
 OMPSRC=		${SRCTOP}/contrib/llvm-project/openmp/runtime/src
 ITTSRC=		${OMPSRC}/thirdparty/ittnotify
 .PATH:		${OMPSRC}
 .PATH:		${ITTSRC}
 
 SRCS+=		ittnotify_static.cpp
 SRCS+=		kmp_affinity.cpp
 SRCS+=		kmp_alloc.cpp
 SRCS+=		kmp_atomic.cpp
 SRCS+=		kmp_barrier.cpp
 SRCS+=		kmp_cancel.cpp
 SRCS+=		kmp_csupport.cpp
 SRCS+=		kmp_debug.cpp
 SRCS+=		kmp_dispatch.cpp
 SRCS+=		kmp_environment.cpp
 SRCS+=		kmp_error.cpp
 SRCS+=		kmp_ftn_cdecl.cpp
 SRCS+=		kmp_ftn_extra.cpp
 SRCS+=		kmp_global.cpp
 SRCS+=		kmp_gsupport.cpp
 SRCS+=		kmp_i18n.cpp
 SRCS+=		kmp_io.cpp
 SRCS+=		kmp_itt.cpp
 SRCS+=		kmp_lock.cpp
 SRCS+=		kmp_runtime.cpp
 SRCS+=		kmp_sched.cpp
 SRCS+=		kmp_settings.cpp
 SRCS+=		kmp_str.cpp
 SRCS+=		kmp_taskdeps.cpp
 SRCS+=		kmp_tasking.cpp
 SRCS+=		kmp_threadprivate.cpp
 SRCS+=		kmp_utility.cpp
 SRCS+=		kmp_version.cpp
 SRCS+=		kmp_wait_release.cpp
 SRCS+=		ompt-general.cpp
 SRCS+=		z_Linux_asm.S
 SRCS+=		z_Linux_util.cpp
 INCS+=		omp.h
 
 WARNS?=		1
 
 CFLAGS+=	-D__STDC_CONSTANT_MACROS
 CFLAGS+=	-D__STDC_FORMAT_MACROS
 CFLAGS+=	-D__STDC_LIMIT_MACROS
 CFLAGS+=	-I${.CURDIR}
 CFLAGS+=	-I${OMPSRC}
 CFLAGS+=	-I${ITTSRC}
 CFLAGS+=	-ffunction-sections
 CFLAGS+=	-fdata-sections
 CXXFLAGS+=	-fvisibility-inlines-hidden
 CXXFLAGS+=	-fno-exceptions
 CXXFLAGS+=	-fno-rtti
+CXXSTD=		c++17
 
 .if ${COMPILER_TYPE} == "clang"
 .if ${MACHINE_CPUARCH} == "i386"
 .if ${COMPILER_VERSION} >= 90000
 # When targeting i386, clang 9.0.0 produces a new warning about large atomic
 # operations "possibly incurring significant performance penalties", but there
 # is not much we can do about it.
 CWARNFLAGS+=	-Wno-atomic-alignment
 .endif
 .if ${COMPILER_VERSION} >= 170000
 # When targeting i386, clang 17.0.0 produces a new warning that __sync
 # builtin operations must have natural alignment, but there is not much we
 # can do about it.
 CWARNFLAGS+=	-Wno-sync-alignment
 .endif # COMPILER_VERSION >= 170000
 .endif # MACHINE_CPUARCH == i386
 .if ${COMPILER_VERSION} >= 180000
 # clang 18.0.0 introduces a new warning about variable length arrays in C++,
 # which OpenMP makes use of in several sources.
 CXXWARNFLAGS+=	-Wno-vla-cxx-extension
 .endif # COMPILER_VERSION >= 180000
 .endif # COMPILER_TYPE == clang
 
 LDFLAGS+=	-Wl,--warn-shared-textrel
 LDFLAGS+=	-Wl,--gc-sections
 LDFLAGS+=	-Wl,-z,noexecstack
 LDFLAGS+=	-Wl,-fini=__kmp_internal_end_fini
 LDFLAGS+=	-Wl,-soname,libomp.so
 
 VERSION_MAP=	${OMPSRC}/exports_so.txt
 
 LIBADD+=	pthread
 LIBADD+=	m
 
 SYMLINKS+=	${SHLIB_NAME} ${LIBDIR}/libgomp.so
 
 .include <bsd.lib.mk>