When enabling or disabling a target we typically need to rebuild most
of LLVM because of the change to the values of the LLVM_HAS_*_TARGET
macros in llvm-config.h, which is included by most of the code, but
are unused by LLVM itself. To avoid this, move the LLVM_HAS_*_TARGET
macros to a separate header, Targets.h.
Update the only in-tree user of the macros (MLIR) to refer to the new
header. I expect that out-of-tree users will detect the change either
at compile time if they build with -Wundef, or at runtime. As far as
I can tell, the usage of these macros is rare in out-of-tree projects,
I found no out-of-tree users in projects indexed by Debian code search
[1], and one user [2] in projects indexed by GitHub code search [3]
(excluding forks of LLVM).
[1] https://codesearch.debian.net/search?q=%23.*LLVM_HAS_.*_TARGET&literal=0
[2] 238706b12b/lib/gc/Target/LLVM/XeVM/Target.cpp (L72)
[3] https://github.com/search?q=%2F%23.*LLVM_HAS_.*_TARGET%2F&type=code
Reviewers: nico, grypp, mstorsjo, MaskRay
Reviewed By: MaskRay
Pull Request: https://github.com/llvm/llvm-project/pull/136388
667209e451