Makefile.lite: Include config.mk from top level build dir

Makefile.lite in libs/executables subdirs must include
top level's config.mk to allow variables defined there (OS, PROC)
to be used; otherwise e.g. EXPLICIT_LIBS is not set and link
fails on Darwin.

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
diff --git a/src/test_libFLAC/Makefile.lite b/src/test_libFLAC/Makefile.lite
index be7c595..e95beb3 100644
--- a/src/test_libFLAC/Makefile.lite
+++ b/src/test_libFLAC/Makefile.lite
@@ -21,6 +21,8 @@
 #
 
 topdir = ../..
+
+include $(topdir)/build/config.mk
 libdir = $(topdir)/objs/$(BUILD)/lib
 
 PROGRAM_NAME = test_libFLAC