xcode_sdk.cmake: Use xcrun to set CMAKE_LINKER

It seems to be unused in our build, but it shouldn't hurt to initialize
it correctly anyway.

git-svn-id: https://llvm.org/svn/llvm-project/test-suite/trunk@294528 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed