LLVM_ENABLE_RUNTIMES=flang-rt for premerge-monolithic-*

[Meinersbur]

Update premerge-monolithic-windows and premerge-monolithic-linux to prepare for the removal of the "projects" build of the flang runtime in llvm/llvm-project#124126.

This does not change the actual premerge GitHub action, which is done by llvm/llvm-project#128678

For premerge-monolithic-linux, add flang-rt to the LLVM_ENABLE_RUNTIMES list, indirectly by adding it to depends_on_projects which also updated the build scheduler.

For premerge-monolithic-windows, remove building flang to match the actual pre-merge build which disabled building flang on Windows in llvm/llvm-project@e4b424a. Adding flang-rt would also require compiler-rt (which was always required on Windows, but now there is a regression test for it) and check-compiler-rt is currently failing.

Split off from #333. Verified to work locally using instruction from https://llvm.org/docs/HowToAddABuilder.html#testing-a-builder-config-locally. With the exception of -gmlt which seems to be a Google-only extention of Clang.

Affected builders:

• premerge-monolithic-windows
• premerge-monolithic-linux

Affected workers:

• premerge-windows-1
• premerge-linux-1

Admins listed for those workers:

• llvm-premerge-buildbots llvm-premerge-buildbots@google.com
• Mikhail Goncharov goncharov.mikhail@gmail.com

[boomanaiden154]

LGTM, assuming that it's fine for FLANG_RT to be in LLVM_ENABLE_PROJECTS.

[Meinersbur]

LGTM, assuming that it's fine for FLANG_RT to be in LLVM_ENABLE_PROJECTS.

zorg will automatically fill enable_runtimes based on depends_on_projects, unless enable_runtimes is specified explicitly. See also https://github.com/llvm/llvm-zorg/pull/383/files and https://github.com/Meinersbur/llvm-zorg/blob/f43eb12c2f993841905651ca5c14fb50929b55f8/zorg/buildbot/process/factory.py#L65-L66

[boomanaiden154]

Ah, okay. Thanks for the explanation. Seems reasonable enough to me.