[llvm] [COFF] Set .llvmbc and .llvmcmd to metadata section (PR #150879)

[Haohai Wen via llvm-commits]

HaohaiWen wrote:

@sbc100, @MaskRay, I'd like to set .llvmbc and .llvmcmd as `Exclude` section for ELF/COFF so that they will be dropped by linker.
Is there any reason to keep them in executable file?

https://github.com/llvm/llvm-project/pull/150879