test for gio

It seems glib added gio in 2.15, though I don't know if svgload will
actually work with a glib that old.

configure.ac

@@ -475,6 +475,16 @@ PKG_CHECK_MODULES(CONTEXT_GET_HELP, glib-2.0 >= 2.14,
   ]
 )
 
+# from 2.15 we have GIO
+PKG_CHECK_MODULES(GIO, glib-2.0 >= 2.15,
+  [AC_DEFINE(HAVE_GIO,1,
+	    [define if your glib has GIO.]
+   )
+  ],
+  [:
+  ]
+)
+
 # from 2.28 we have a monotonic timer
 PKG_CHECK_MODULES(MONOTONIC_TIME, glib-2.0 >= 2.28,
   [AC_DEFINE(HAVE_MONOTONIC_TIME,1,
@@ -508,6 +518,8 @@ PKG_CHECK_MODULES(THREADS, glib-2.0 >= 2.32,
    AC_DEFINE(HAVE_VALUE_GET_SCHAR,1,
 	     [define if your glib has g_value_get_schar().]
    )
+  ],
+  [:
   ]
 )
 

libvips/foreign/svgload.c

@@ -67,7 +67,12 @@
 #include <vips/internal.h>
 #include <vips/debug.h>
 
-#ifdef HAVE_RSVG
+/* We need GIO for GInputStream.
+ */
+
+#if defined(HAVE_RSVG) && defined(HAVE_GIO)
+
+#include <gio/gio.h>
 
 /* A GInputStream that's actually a VipsStreami under the hood. This lets us
  * hook librsvg up to libvips using the GInputStream interface.
@@ -1002,7 +1007,7 @@ vips_foreign_load_svg_buffer_init( VipsForeignLoadSvgBuffer *buffer )
 {
 }
 
-#endif /*HAVE_RSVG*/
+#endif /*HAVE_RSVG && HAVE_GIO*/
 
 /**
  * vips_svgload:

libvips/include/vips/vips.h

@@ -88,7 +88,6 @@ extern "C" {
 #include <glib/gstdio.h>
 #include <gmodule.h>
 #include <glib-object.h>
-#include <gio/gio.h>
 
 /* If we're being parsed by SWIG, remove gcc attributes.
  */