scanner: Don't link to -lgirepository when dumping

This helps us avoid a problematic case where in say jhbuild, using
a system (/usr/lib) glib, adding in -l girepository-1.0 will inject
-L /path/to/builddir, when we don't want that.

https://bugzilla.gnome.org/show_bug.cgi?id=630342

Makefile.am

@@ -53,7 +53,7 @@ libgirepository_1_0_la_SOURCES =		\
 	giunioninfo.c				\
 	givfuncinfo.c
 
-libgirepository_1_0_la_CPPFLAGS = $(GIREPO_CFLAGS)
+libgirepository_1_0_la_CPPFLAGS = $(GIREPO_CFLAGS) -DG_IREPOSITORY_COMPILATION
 libgirepository_1_0_la_LIBADD = $(GIREPO_LIBS)
 libgirepository_1_0_la_LDFLAGS = -no-undefined -version-number 1:0:0
 
@@ -69,3 +69,5 @@ libgirepository_parser_la_SOURCES =		\
 	girwriter.h
 libgirepository_parser_la_CFLAGS = $(GIREPO_CFLAGS)
 
+gdumpdir = $(datadir)/gobject-introspection-1.0/
+gdump_DATA = gdump.c

gdump.c

@@ -24,8 +24,15 @@
 #include <glib-object.h>
 #include <gio/gio.h>
 
-#include "girepository.h"
+/* This file is both compiled into libgirepository.so, and installed
+ * on the filesystem.  But for the dumper, we want to avoid linking
+ * to libgirepository; see
+ * https://bugzilla.gnome.org/show_bug.cgi?id=630342
+ */
+#ifdef G_IREPOSITORY_COMPILATION
 #include "config.h"
+#include "girepository.h"
+#endif
 
 #include <string.h>