arm: enable ssp

[mhorne]

Summary

With current generation clang/llvm it can pass all of our tests in
libc/ssp.

While here, remove the extra MACHINE_CPUARCH check for mips. The SSP
option is marked BROKEN on this architecture in bsd.opts.mk, which is
enough to ensure normal builds won't set SSP_CFLAGS.

[emaste]

Nice cleanup, and BROKEN_OPTIONS or default off is better than distributed special cases.

share/mk/bsd.sys.mk

 CFLAGS.clang+=   -Qunused-arguments
 # The libc++ headers use c++11 extensions.  These are normally silenced because
 # they are treated as system headers, but we explicitly disable that warning
 # suppression when building the base system to catch bugs in our headers.
 # Eventually we'll want to start building the base system C++ code as C++11,
 # but not yet.
 CXXFLAGS.clang+=         -Wno-c++11-extensions
 
-.if ${MK_SSP} != "no" && \
-    ${MACHINE_CPUARCH} != "arm" && ${MACHINE_CPUARCH} != "mips"
+.if ${MK_SSP} != "no"
 # Don't use -Wstack-protector as it breaks world with -Werror.
 SSP_CFLAGS?=    -fstack-protector-strong
 CFLAGS+=        ${SSP_CFLAGS}
-.endif # SSP && !ARM && !MIPS
+.endif # SSP
 
 # Additional flags passed in CFLAGS and CXXFLAGS when MK_DEBUG_FILES is
 # enabled.
 DEBUG_FILES_CFLAGS?= -g
 
 # Allow user-specified additional warning flags, plus compiler and file
 # specific flag overrides, unless we've overridden this...
 .if ${MK_WARNS} != "no"

sys/conf/kern.mk

 # use of signed integer wraparound mechanics so we need the compiler
 # to treat it as a wraparound and not take shortcuts.
 #
 CFLAGS+=        -fwrapv
 
 #
 # GCC SSP support
 #
-.if ${MK_SSP} != "no" && \
-    ${MACHINE_CPUARCH} != "arm" && ${MACHINE_CPUARCH} != "mips"
+.if ${MK_SSP} != "no"
 CFLAGS+=        -fstack-protector
 .endif
 
 #
 # Retpoline speculative execution vulnerability mitigation (CVE-2017-5715)
 #
 .if defined(COMPILER_FEATURES) && ${COMPILER_FEATURES:Mretpoline} != "" && \
     ${MK_KERNEL_RETPOLINE} != "no"