The tests in pixbuf-lowmem.c has undefined references to __libc_malloc
and __libc_free, so skip building tests.

diff -u -r ../gdk-pixbuf-2.31.7/Makefile.in ./Makefile.in
--- ../gdk-pixbuf-2.31.7/Makefile.in	2015-09-01 07:46:31.000000000 -0400
+++ ./Makefile.in	2015-09-07 10:48:15.299336025 -0400
@@ -448,7 +448,7 @@
 top_build_prefix = @top_build_prefix@
 top_builddir = @top_builddir@
 top_srcdir = @top_srcdir@
-SUBDIRS = gdk-pixbuf po docs tests contrib build
+SUBDIRS = gdk-pixbuf po docs contrib build
 EXTRA_DIST = \
 	config.h.win32 		\
 	glib-tap.mk		\