Enable Flang-RT for all Flang builders.

[Meinersbur]

Modify all build configurations that build Flang to also build Flang-RT. Flang-RT is the runtime component of Flang that is refactored into its own runtime project in llvm/llvm-project#110217.

The following classes of builder are affected:

• Builders with LLVM_ENABLE_PROJECTS=flang and running check-flang: Adding LLVM_ENABLE_RUNTIMES=flang-rt and check-flang-rt. These builders would continue to be green after [Flang] LLVM_ENABLE_RUNTIMES=flang-rt llvm-project#110217 even without this PR, just testing less.

• Clang builders with checkout_flang=True: Automatically add flang-rt to depends_on_projects which also adds LLVM_ENABLE_PROJECTS with enable_runtimes="auto". These builders would continue to be green after [Flang] LLVM_ENABLE_RUNTIMES=flang-rt llvm-project#110217 even without this PR, just testing less.

• Clang builders with checkout_flang=True and runTestSuite=True: Running the the test-suite with Flang requires Flang-RT, so these builders would start failing with [Flang] LLVM_ENABLE_RUNTIMES=flang-rt llvm-project#110217 without this PR.

• linaro-flang-aarch64-out-of-tree: Has its own build factory that would require larger changes to also check/run Flang-RT. Should stay green even after [Flang] LLVM_ENABLE_RUNTIMES=flang-rt llvm-project#110217.

• flang-runtime-cuda-gcc: Only compiles but does not run check. Used to be a flang/runtime out-of-tree build. Runtime-only builds of Flang-RT needs the path to flang. I do not know where/whether this can be found on the workers so changing it to a bootstrap build. More important to keep the buildbots green.

• flang-runtime-cuda-clang: Staged build of first compiling LLVM+Clang, then Flang out-of-tree. With this PR also building Flang in-tree and Flang-RT as runtime-only build. Building both Flang and Flang-RT out-of-tree would require another stage, but "linaro-flang-aarch64-out-of-tree" is already testing the Flang out-of-tree build.

[Meinersbur]

@gkistanova The get the buildsbots green after pushing llvm/llvm-project#110217, pushing this PR and restarting the buildbot master would be time-critical. Is it possible to schedule these things together so we can minimize the time the buildbots are failing?