[Sema] Fix PR28181 by avoiding calling BuildOverloadedBinOp in C mode

rdar://28532840

Differential Revision: https://reviews.llvm.org/D25213

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@292497 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit dbbfaa60fd51404ce1710705bb096ee214dc5622)
2 files changed