[flang-commits] [flang] [llvm] [Premerge] Add flang-rt (PR #128678)

[Michael Kruse via flang-commits]

Meinersbur wrote:

I verified it locally. I also removed changes that I think are not strictly needed. So now whenever `flang` is built, `flang-rt` is built as well. `CMAKE_Fortran_COMPILER` is added to point to the Fortran compiler in the runtimes built. If flang is not being built, it is ignored by CMake.

I also added a small change to the `flang/` directory to trigger a pre-merge built of flang, to actually test it.

Some Background: In its current form #124126 will implicitly add LLVM_ENABLE_RUNTIMES=flang-rt (unless specifying `FLANG_ENABLE_FLANG_RT=OFF` that is). That is, the pre-merge will build flang-rt anyway at that point, but using the bootstrapping build and without `check-flang-rt`. For the pre-merge build this means that we get an ugly mix of bootstrapping-build of flang-rt and a runtimes-standalone build of libcxx,libcxxabi,libunwind at the same time. I am proactively adapting the buildbots to not have unfortunate surprises when #124126 is pushed, having to handle all at once / repeated reverts.

If you think that would be the lesser evil, I would be OK with skipping this PR.

https://github.com/llvm/llvm-project/pull/128678