[Lexer] Improve Lexer::getSourceText() when the given range deals with function macro arguments.

This is a modified version of a patch by Manuel Klimek.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@182055 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed