cmake: fixed gflags namespace detection (fixes #193)

This commit fixes gflags namespace detection using Intel compiler and ensures
the generated try_compile command line does not produce malformed paths.

cmake/DetermineGflagsNamespace.cmake

@@ -35,7 +35,7 @@ int main(int argc, char**argv)
         "${CMAKE_BINARY_DIR}" "${_check_file}"
         COMPILE_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS}" -DGFLAGS_NAMESPACE=${_namespace}
         LINK_LIBRARIES "${gflags_LIBRARIES}"
-        CMAKE_FLAGS -DINCLUDE_DIRECTORIES:STRING="${gflags_INCLUDE_DIR}"
+        CMAKE_FLAGS -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE} "-DINCLUDE_DIRECTORIES:STRING=${gflags_INCLUDE_DIR}"
         OUTPUT_VARIABLE OUTPUT)
 
       if (${VARIABLE})