gdk-pixbuf: fix static build with libtiff

Fixes:
http://autobuild.buildroot.net/results/ce6/ce61d5aaf5dfdda92fcecb08a30b6093926d6f01/
http://autobuild.buildroot.net/results/76b/76b550da06fe547716f089e46d96a1406043268a/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gdk-pixbuf/gdk-pixbuf.mk

@@ -33,7 +33,9 @@ endif
 ifneq ($(BR2_PACKAGE_TIFF),y)
 GDK_PIXBUF_CONF_OPTS += --without-libtiff
 else
-GDK_PIXBUF_DEPENDENCIES += tiff
+GDK_PIXBUF_DEPENDENCIES += tiff host-pkgconf
+GDK_PIXBUF_CONF_ENV += \
+	LIBS='$(shell $(PKG_CONFIG_HOST_BINARY) --libs libtiff-4)'
 endif
 
 ifeq ($(BR2_PACKAGE_XLIB_LIBX11),y)