[llvm] [BOLT] Enable cross compilation of runtime libraries (PR #101180)

[Gergely Bálint via llvm-commits]

bgergely0 wrote:

> We don't want to introduce dependencies on host cross-compilers all the while Clang can be used for that purpose. We can add the dependency on Clang for cross-target runtimes build if necessary, as we already do for BOLT tests.

@aaupov @petrhosek

Hi! 
I'll check runtimes more thorougly, but I am not sure what you mean by introducing dependencies on host cross-compilers. My code only _allows_ using other cross compilers if they are available (and clang isn't), it is not a dependency. By default we expect the user to use clang for cross compilation. 
Any dependence on host cross compilers is after an `elseif`:
```cmake
    if(CMAKE_C_COMPILER_ID MATCHES ".*Clang.*" AND CMAKE_CXX_COMPILER_ID MATCHES ".*Clang.*")
      bolt_rt_target_supported_clang(${tgt} supported)

    elseif(CMAKE_C_COMPILER_ID MATCHES ".*GNU.*" AND CMAKE_CXX_COMPILER_ID MATCHES ".*GNU.*")
      bolt_rt_target_supported_gnu(${tgt} supported)
    endif()
```

Could you clarify what do you mean by dependency?
Thanks!



https://github.com/llvm/llvm-project/pull/101180