[UBSan] Add report deduplication for -fsanitize=function.

Summary:
Make sure we don't print the error report from -fsanitize=function
twice for the same source location, as we do in another UBSan handlers.

Test Plan: check-ubsan test suite

Reviewers: rsmith, pcc

Reviewed By: pcc

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D7524

llvm-svn: 228772