[CMake][compiler-rt] Don't load LLVM config in the runtimes build

LLVM runtimes build already loads the LLVM config and sets all
appropriate variables, no need to do it again.

Differential Revision: https://reviews.llvm.org/D137870

GitOrigin-RevId: 9c2700dfa51a3f10e47f902939bbbe0a5b6b9c9b
2 files changed