Use the appropriate SourceLocation for the template backtrace when doing
template argument deduction.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198995 91177308-0d34-0410-b5e6-96231b3b80d8
Add a new attribute 'enable_if' which can be used to control overload resolution based on the values of the function arguments at the call site.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198996 91177308-0d34-0410-b5e6-96231b3b80d8