llvm-cov: add test for report's function & file association.

This commit adds a test which checks that the functions defined in header files will get associated with the header files rather than the source files in the reports.

Differential Revision: http://reviews.llvm.org/D5489


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218673 91177308-0d34-0410-b5e6-96231b3b80d8