[Flang][OpenMP] Move builtin .mod generation into runtimes

[Meinersbur]

Experiments for per-target builtin modules

[jhuber6]

What's the main limitation here? If this is just a file dependency it should be identical to how all the OpenMP tests depend on omp.h being in the resource directory. IMHO this is trivial if we do a runtimes build, since we can just require that openmp;flang-rt are in the same toolchain, which then gives us well defined access to openmp's CMake targets so long as it's listed before flang-rt.

[jhuber6]

Shouldn't this be implied by the user specifying it below?

[Meinersbur]

-fintrinsic-modules-path is defined by gfortran, but flang's interpretation is incompatible (Even though they copy-pasted gfortran's help description). -fbuiltin-modules-path= is the temporary replacement. At the end, I hope I will not need either of them, by fixing -fintrinsic-modules-path.

[jhuber6]

Format.

[jhuber6]

Suggested change

	if (D.IsFlangMode()) {
	getIntrinsicModulePaths().append(getIntrinsicModulePaths());
	}
	if (D.IsFlangMode())
	getIntrinsicModulePaths().append(getIntrinsicModulePaths());

[Meinersbur]

While I appreciate the review, it is not yet in the state that warants one. It is still in an experimentation stage, so I did not yet care about formatting. There are also a lot of changes in here that will eventually not be needed.

Goals are:

1. Currently modules files are expected at $prefix/include/flang/*.mod where prefix is the parent of bin where flang is located. It should be in $prefix/lib/clang/finclude/<triple>/*.h, i.e. the resource directory since mod-files are specific to the version of flang, and distinct for each target triple since the mod files can be different for each target. Necessary for cross-compilation. In addition to the CMake code, the flang driver code needs to change as well because it hardcodes $path/../include/flang.

2. Use cmake to build the module files within the flang-rt/ runtime. The LLVM_ENABLE_RUNTIMES system handles which target triples to build and Flang being available. CMake should care about the build dependencies. Have to change the driver again to tell it where to emit the module files.

3. Use the same mechanism as above to build omp_lib.mod and omp_lib_kinds.mod, but in the openmp/ runtime. Since in the same CMake builddir, CMake will ensure dependencies already.

4. This means flang-rt (and openmp) is necessary to be compiled before running flang's tests which require those module files. Flang's OpenMP tests already require openmp's modules to be compiled, it will be no different to flang-rt's builtin modules.

Sounds relatively simple, but there have been many small issues, starting with CMake's misspelling of CMAKE_Fortran_BUILDING_INSTRINSIC_MODULES.

[DanielCChen]

1. It should be in $prefix/lib/clang/finclude/<triple>/*.h

Just want to make sure: Should it be $prefix/lib/clang/${LLVM_VERSION_MAJOR}/finclude/<triple>/*.mod?

[Meinersbur]

Just want to make sure: Should it be $prefix/lib/clang/${LLVM_VERSION_MAJOR}/finclude/<triple>/*.mod?

That is correct, I forgot the version number that is part of the resource directory.