Refactor some code to use the IRBuilder.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173467 91177308-0d34-0410-b5e6-96231b3b80d8
Use xcrun to find the right compiler when building llvmCore. <rdar://12801151>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173468 91177308-0d34-0410-b5e6-96231b3b80d8