[compiler-rt] Properly detect lack of available system libraries for arch in clang_darwin.mk

Summary: This is the Makefile analog of r247833, except that the test also had to be changed such that clang actually attempts to link the program as opposed to just building it. Because of that change, I also switched the order to checking for ld/clang architecture support, because now lack of ld support would make the clang check fail. This fixes PR24776.

Reviewers: beanz

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D13425

llvm-svn: 249358