scanner: Use packages from --pkg

Use pkgconfig files from --pkg when compiling the dump binary.

This helps avoiding linker errors when init sections are provided that
use code from those packages.

https://bugzilla.gnome.org/show_bug.cgi?id=639039

giscanner/dumper.py

@@ -87,6 +87,7 @@ def __init__(self, options, get_type_functions):
         self._uninst_srcdir = os.environ.get(
             'UNINSTALLED_INTROSPECTION_SRCDIR')
         self._packages = ['gio-2.0 gthread-2.0']
+        self._packages.extend(options.packages)
 
     # Public API