The easier way to create a correct Makefile.PL is to copy it from another module. The following steps show how I create one for Gtk::ExText.
copy ../GtkGLArea/Makefile.PL .
replace all string 'GladeXML' by 'ExText'
replace $inc and $libs with
$inc = '-I/usr/local/include ' . `gtk-config --cflags` ; chomp($inc); $libs = "-L/usr/local/lib -lgtkextext " . `gtk-config --libs`;
remove line 'add_boot' and add_raw_xs(['xs/GtkGdk.xs','xs/Constants.xs']);
remove the following lines
$pm->{ 'Constants.pm' } = '$(INST_LIBDIR)/ExText/Constants.pm';
$pm->{ 'Glut.pm'} = '$(INST_LIBDIR)/ExText/Glut.pm';change
add_header(qw( <gtkgl/gtkglarea.h> ));
to
add_header(qw( <gtkextext.h> ));
The result Makefile.PL can be found at ......