[compiler-rt] Build bitcode libclang_rt.builtins for GPU targets (PR #189340)

[via llvm-commits]

jinge90 wrote:

Hi, @jhuber6 
I want to consult with you about building llvm .bc format compiler-rt builtin library for GPU targets. Currently, we can build static archive compiler-rt builtin/profile library consisting of bitcode files for GPU, it seems that providing .bc format library can   also bring some benefit:
1. We can re-use 'mlink-builtin-bitcode' option to link the library in device compilation phase for GPU
2. We can align with libc for GPU which also provides libc.bc and libm.bc.
Could you help review this PR and provide your insight when having time?
Thanks very much.

https://github.com/llvm/llvm-project/pull/189340