This change force us to use the top-level CMake's detected tools. We
need to do this as a temporary workaround as when using CMake
versions >= 3.22 we'll pickup the built llvm-ranlib by default if it's
in the path (which it is when doing a sub build via
llvm_ExternalProject_Add for the runtimes).
llvm-ranlib runs into problems on AIX due to missing 64-bit
functionality to be added by
https://reviews.llvm.org/D142479 and https://reviews.llvm.org/D142660.
Once those patches land, this can be reverted.
Differential Revision: https://reviews.llvm.org/D142727