Revert "Re-apply "[CMake][compiler-rt][AArch64] Avoid preprocessing LSE builtins separately""

This reverts commit 03ebe1937192c247c4a7b8ec19dde2cf9845c914.

It's still breaking bots, e.g. http://green.lab.llvm.org/green/job/clang-stage1-RA/17027/console although it doesn't change any actual code.
The compile errors don't make much sense either. Revert for now.

Differential Revision: https://reviews.llvm.org/D93228