Make gobject-introspection warnings non-fatal
https://bugs.webkit.org/show_bug.cgi?id=115184

Reviewed by Carlos Garcia Campos.

* GNUmakefile.am: Make it so that gobject-introspection errors do not fail the buld
until we get to a point where gobject-introspection gives consistent warnings.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149118 268f45cc-cd09-0410-ab3c-d52691b4dbfc