Pass GTEST_ROOT and GMOCK_ROOT through to distcheck.

So that they don't have to be exported in the environment if they're needed.

common/cmake_modules/MakeDistCheck.cmake

@@ -50,6 +50,8 @@ FUNCTION(RUN_DIST_CHECK PACKAGE_PREFIX EXT)
               -D CMAKE_CXX_FLAGS=${CMAKE_CXX_FLAGS}
               -D CMAKE_PREFIX_PATH=${CMAKE_PREFIX_PATH}
               -D CMAKE_INSTALL_PREFIX=../${INSTALL_DIR}
+              -D GTEST_ROOT=${GTEST_ROOT}
+              -D GMOCK_ROOT=${GMOCK_ROOT}
               ../${PACKAGE_PREFIX}
             WORKING_DIRECTORY ${BUILD_DIR}
             ERROR_MSG "CMake configure command failed."