Makefile.inc1: Build clang-tblgen when MK_LLVM_BINUTILS_BOOTSTRAP=yes

[0mp]

Summary

Consider building world for riscv/riscv64 on an arm64/aarch64 host with
the following command:

make buildworld -DNO_ROOT \
	DESTDIR=/home/0mp/bricoler/freebsd-src-build/stage.riscv.riscv64 \
	METALOG=/home/0mp/bricoler/freebsd-src-build/stage.riscv.riscv64/METALOG.buildworld.mtree \
	TARGET=riscv \
	TARGET_ARCH=riscv64 \
	KERNCONF=GENERIC \
	WITH_REPRODUCIBLE_BUILD=yes \
	WITH_CCACHE_BUILD=yes \
	WITHOUT_CLEAN= \
	WITHOUT_CLANG= \
	WITHOUT_LLD= \
	WITHOUT_LLDB= \
	WITHOUT_LIB32= \
	WITHOUT_ZFS_TESTS=

The build errors out during "stage 3: cross tools" when building
"lib/clang/libclang (all)":

*** Failed target: clang/AST/AbstractBasicWriter.inc
*** In directory: /home/0mp/src/lib/clang/libclang
*** Failed commands:
        ${CLANG_TBLGEN} -gen-clang-basic-writer  -I ${CLANG_SRCS}/include -d ${.TARGET:C/$/.d/} -o ${.TARGET}  ${CLANG_SRCS}/include/clang/AST/PropertiesBase.td
        => clang-tblgen -gen-clang-basic-writer  -I /home/0mp/src/contrib/llvm-project/clang/include -d clang/AST/AbstractBasicWriter.inc.d -o clang/AST/AbstractBasicWriter.inc  /home/0mp/src/contrib/llvm-project/clang/include/clang/AST/PropertiesBase.td
*** [clang/AST/AbstractBasicWriter.inc] Error code 127

It seems that clang-tblgen is not available to lib/clang/libclang.
In fact, clang-tblgen is nowhere to be found in the build artifacts.
find ~/bricoler -name '*clang-tblgen* returns nothing.

An immediate workaround is to build without WITHOUT_CLANG.

However, there must be a better way.

It turns out that

clang_tblgen+= usr.bin/clang/clang-tblgen

gets added to the bootstrap-tools target during the cross-tools target
pass of Makefile.inc1 (thanks to MK_CLANG=yes). This is sadly too late.

What would help is to plug clang-tblgen to bootstrap-tools when

${MK_LLVM_BINUTILS_BOOTSTRAP} != "no" || ${MK_LLVM_BINUTILS} != "no"

but I'm not sure if that's correct.

Let's consider the if statements surrounding _clang_libs:

.if ${MK_CLANG_BOOTSTRAP} != "no" || ${MK_LLD_BOOTSTRAP} != "no" || \
    ${MK_LLVM_BINUTILS_BOOTSTRAP} != "no"
_clang_libs=    lib/clang
.endif

Perhaps adding

${MK_LLVM_BINUTILS_BOOTSTRAP} != "no"

to clang-tblgen if statement is not wrong:

.if ${MK_CLANG_BOOTSTRAP} != "no" || ${MK_CLANG} != "no" || \
    ${MK_LLDB} != "no" || ${MK_LLVM_BINUTILS_BOOTSTRAP} != "no"
_clang_tblgen+= lib/clang/libclangminimal
_clang_tblgen+= usr.bin/clang/clang-tblgen
.endif

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