[compiler-rt] r276256 - Attempt to fix clang-cmake-mips after r268977.

[Daniel Sanders via llvm-commits]

> > > What I think is happening is that the 'include(builtin-config-ix)' in lib/builtins/CMakeLists.txt includes the
> > > 'set(TEST_COMPILE_ONLY On)' from cmake/builtin-config-ix.cmake which later causes
> > > CAN_TARGET_mips64 to be set according to the compiler behaviour rather than the compiler+linker
> > > behaviour. I can compile mips64 objects successfully on this machine but I can't link them.
> > 
> > This isn't what's happening but because 'set(TEST_COMPILE_ONLY On)' executes slightly after the CAN_TARGET_mips64 check.
> > 
> > It seems the truth of the matter is that r275780 on Monday fixed gcc builds by changing –mabi=n64 to –mabi=64. This didn't
> > take effect until Wednesday because buildbot is configured to skip the cmake command if build.ninja exists. On Wednesday,
> > we repaired the disk which eventually caused buildbot to wipe the build area and run the cmake command, introducing the
> > failures. At this point, I couldn't find anything obvious in the blamelists for Wednesday so I looked into it and found the
> > unconditional 'set(TEST_COMPILE_ONLY On)' which led me to r276256.
> > 
> > To summarize, I think the unconditional 'set(TEST_COMPILE_ONLY On)' is probably a bug that would have a similar effect to our buildbot failure but it wasn't the cause of it. Sorry for the noise.
> 
> This is actually intentional. It shouldn't impact the non-darwin build because the tests on the non-Apple branch are under if(COMPILER_RT_BUILTINS_STANDALONE_BUILD). In the Apple build, this
> allows the builtins build to include architectures that aren't included in the sanitizer build.
> 
> -Chris

Ah ok. Do you expect to define CAN_TARGET_${arch} both before and after the 'set(TEST_COMPILE_ONLY On)' or just on one side of it? If the answer is both then I'll need to re-work this workaround since the checks after the 'set(TEST_COMPILE_ONLY On)' will currently re-use the cached CAN_TARGET_${arch} from before it and this won't account for the updated TEST_COMPILE_ONLY.