Add a missing CMake config file into the tarball.

This commit was SVN r25687.

contrib/Makefile.am

@@ -116,6 +116,7 @@ EXTRA_DIST = \
         platform/win32/CMakeModules/get_c_alignment.cmake \
         platform/win32/CMakeModules/list_subdirs.cmake \
         platform/win32/CMakeModules/ompi_check_Microsoft.cmake \
+        platform/win32/CMakeModules/ompi_check_MinGW.cmake \
         platform/win32/CMakeModules/ompi_configure.cmake \
         platform/win32/CMakeModules/ompi_find_type.cmake \
         platform/win32/CMakeModules/opal_event_config.cmake \