test/librt: make it build again

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

test/librt/Makefile

@@ -1,6 +1,9 @@
 # uClibc shm tests
 # Licensed under the LGPL v2.1, see the file COPYING.LIB in this tarball.
 
+top_builddir=../../
+include ../Rules.mak
+-include Makefile.in
 include ../Test.mak
 
 LDFLAGS_shmtest := -lrt