switch IRBuilder to use NewDebugLoc for locations instead

switch IRBuilder to use NewDebugLoc for locations instead
of raw mdnodes.  This allows frontends to specify debug
locations without ever creating an MDNode for the DILocation.

This requires a corresponding clang/llvm-gcc change which
I'll try to commit as simultaneously as possible.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100095 91177308-0d34-0410-b5e6-96231b3b80d8