[Vala] vala-gen-introspect glibconfig.h

[Filip Krynicki <filipkrynicki gmail com>]

I'm trying to generate a VAPI file for gimp 2.7.3, but while performing the
vala-gen-introspect step I'm running into an issue where glibconfig.h
cannot be found. I suspect this is as a result of the file being moved in a
recent glib release - the fix recommended online is to change includes. Is
there some way to modify the INCLUDE variable where vala-gen-introspect
will search for header files?

Thanks,
Fil Krynicki