Hi,
Building Mesa 20.0.x with llvm 10 fails with something that appears to be a bug in llvm itself:

/usr/bin/ld: /usr/lib/llvm-10/lib/libclangCodeGen.a(BackendUtil.cpp.o): in function (anonymous namespace)::EmitAssemblyHelper::EmitAssemblyWithNewPassManager(clang::BackendAction, std::unique_ptr<llvm::raw_pwrite_stream, std::default_delete<llvm::raw_pwrite_stream> >)': (.text._ZN12_GLOBAL__N_118EmitAssemblyHelper30EmitAssemblyWithNewPassManagerEN5clang13BackendActionESt10unique_ptrIN4llvm17raw_pwrite_streamESt14default_deleteIS5_EE+0x1f15): undefined reference to getPollyPluginInfo()'
collect2: error: ld returned 1 exit status

I've tried with rc3/rc4 and rc5 plus https://reviews.llvm.org/D74464