Tidy up CGCXXABI creation

'create' functions conventionally return a pointer, not a reference.

Also use an OwningPtr to get replace the delete of a reference member.

No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198126 91177308-0d34-0410-b5e6-96231b3b80d8
Rename isBuiltinCall() to getBuiltinCallee()

This better describes what the function does.

Cleanup only.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198127 91177308-0d34-0410-b5e6-96231b3b80d8
Briefly document diag-build.sh

It may be a quick and dirty script but it's still useful to have some
indication as to its purpose.

Text taken straight from Jordan's r158682 commit message.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198128 91177308-0d34-0410-b5e6-96231b3b80d8