COpenCOmbineHelpers: add an explicit modulemap

Introduce an explicit modulemap as not all build systems will write out
a modulemap for you.  Add the explicit modulemap to allow building with
alternative build systems.

Sources/COpenCombineHelpers/include/module.modulemap

@@ -0,0 +1,3 @@
+module COpenCombineHelpers {
+  header "COpenCombineHelpers.h"
+}