CSQLite: add module.modulemap

Add a modulemap for this module to allow SPM to build only the tests
against the CMake generated products which are distributed as part of
the toolchain image.

Author: compnerd

Sources/CSQLite/include/module.modulemap

@@ -0,0 +1,5 @@
+
+module SwiftToolchainCSQLite {
+  header "sqlite3.h"
+  header "sqlite3ext.h"
+}