[Driver] Search compiler-rt paths in -print-file-name=

This makes it possible to print the name of compiler-rt libraries
by using simply clang -print-file-name=libclang_rt.${runtime}-${arch}.so
same as other libraries, without having to know the details of the
resource directory organization.

Differential Revision: https://reviews.llvm.org/D35820

llvm-svn: 310548