Summary: This fixes cross-builds with MinGW from case-sensitive file-systems (on Linux)
This is a cherry-pick from
https://github.com/google/benchmark/pull/840
8e48105d46
Original patch by: @jschueller (Julien Schueller) !
Differential Revision: https://reviews.llvm.org/D61371
llvm-svn: 367356