Update introspection.m4

This one includes the INTROSPECTION_MAKEFILE variable
which we will include in all Makefiles which are going
to build introspection girs/typelibs

m4/introspection.m4

@@ -61,6 +61,7 @@ m4_define([_GOBJECT_INTROSPECTION_CHECK_INTERNAL],
        INTROSPECTION_TYPELIBDIR="$($PKG_CONFIG --variable=typelibdir gobject-introspection-1.0)"
        INTROSPECTION_CFLAGS=`$PKG_CONFIG --cflags gobject-introspection-1.0`
        INTROSPECTION_LIBS=`$PKG_CONFIG --libs gobject-introspection-1.0`
+       INTROSPECTION_MAKEFILE=`$PKG_CONFIG --variable=datadir gobject-introspection-1.0`/gobject-introspection-1.0/Makefile.introspection
     fi
     AC_SUBST(INTROSPECTION_SCANNER)
     AC_SUBST(INTROSPECTION_COMPILER)
@@ -69,6 +70,7 @@ m4_define([_GOBJECT_INTROSPECTION_CHECK_INTERNAL],
     AC_SUBST(INTROSPECTION_TYPELIBDIR)
     AC_SUBST(INTROSPECTION_CFLAGS)
     AC_SUBST(INTROSPECTION_LIBS)
+    AC_SUBST(INTROSPECTION_MAKEFILE)
 
     AM_CONDITIONAL(HAVE_INTROSPECTION, test "x$found_introspection" = "xyes")
 ])