Darwin: use the compiler-provided linker

When actually compiling we use clang for the final .dylib creation stage, so we
should ask it what linker it'll use when detecting support for our
architectures.

llvm-svn: 201845

compiler-rt/make/platform/clang_darwin.mk

@@ -46,7 +46,7 @@ XCRunSdkPath = \
 ###
 
 CC       := $(call XCRun,clang)
-LD       := $(call XCRun,ld)
+LD       := $(shell $(CC) -print-prog-name=ld)
 AR       := $(call XCRun,ar)
 RANLIB   := $(call XCRun,ranlib)
 STRIP    := $(call XCRun,strip)