This fixes a number of issues introduced in #97130 when
LLVM_LIBDIR_SUFFIX is a non-empty string. Make sure that the libdir is
always referenced as `lib${LLVM_LIBDIR_SUFFIX}`, not as just `lib` or
`${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}`.
This is the standard libdir convention for all LLVM subprojects. Using
`${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}` would result in a
duplicate suffix.
3c42a77456