Tolerate negative offset when matching sample profile.

Tolerate negative offset when matching sample profile.

In some cases (as illustrated in the unittest), lineno can be less than the heade_lineno because the function body are included from some other files. In this case, offset will be negative. This patch makes clang still able to match the profile to IR in this situation.

http://reviews.llvm.org/D13914

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250873 91177308-0d34-0410-b5e6-96231b3b80d8