[compiler-rt] Use ld64 flag -lto_library instead of DYLD_LIBRARY_PATH

Makes

 bin/llvm-lit \
  projects/compiler-rt/test/profile/Profile-arm64/instrprof-darwin-dead-strip.c

pass on my machine.

Without this change, ld64 complains that the bitcode was generated by LLVM 15
while the reader is 13.1 -- the version of Xcode on my machine. Looks like the
DYLD_LIBRARY_PATH technique isn't working.

-lto_library was added back in ld64-136, which was in Xcode 4.6, which was
released over 10 years ago. So relying on it should be safe by now.

Differential Revision: https://reviews.llvm.org/D124018