glib-gen.mak: Use #include "header" instead of #include <header> for the generated enum C files as the file will alwa...

Original commit message from CVS:
* glib-gen.mak:
Use #include "header" instead of #include <header> for the generated
enum C files as the file will always be in the same directory and
some compilers seem to be a bit strict about that unless . is added
to the include path.
Include all headers that were used to generate the source files in
the C file as they're used there.