First I'll quickly cover generating my Makefile. When I do exactly as you instructed I get this output for generating my Makefile:
Including ApiDoc pod...
Deleting Glib::Object::_LazyLoader from doc.pl's $data
Deleting Glib from doc.pl's $data
Writing build/IFiles.pm
Note (probably harmless): No library found for -lgobject-2.0
Note (probably harmless): No library found for -lglib-2.0
Note (probably harmless): No library found for -lintl
Note (probably harmless): No library found for -lgthread-2.0
Writing Makefile for Glib
...but when I use CPAN to generate the makefile, which explicitly passes a more complete set of include and lib paths to Makefile.PL (because of the program I've mentioned earlier) I get this output:
Including ApiDoc pod...
Deleting Glib::Object::_LazyLoader from doc.pl's $data
Deleting Glib from doc.pl's $data
Writing build/IFiles.pm
Checking if your kit is complete...
Looks good
Writing Makefile for Glib
Which has none of the "No library found" warnings. So I'll continue with the CPAN generated Makefile.