Fix for stringized function-macro args continued across lines

Fix for stringized function-macro args continued across lines

In case of certain #define'd macros, there's a space just before line continuation
that the minimized-source lexer was missing to include, resulting in invalid stringize.

Patch by: kousikk (Kousik Kumar)

Differential Revision: https://reviews.llvm.org/D67635

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@372360 91177308-0d34-0410-b5e6-96231b3b80d8