GCC compatibility: Ignore -finput_charset=UTF-8 argument. It is the default in Clang.

Currently, we fail with an error.

Reviewers: rafael

Reviewed By: rafael

Subscribers: rnk, cfe-commits

Differential Revision: http://reviews.llvm.org/D4347

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212110 91177308-0d34-0410-b5e6-96231b3b80d8