selftests/vm: fix link error for transhuge-stress test

add -lrt to fix undefined reference to `clock_gettime'
error seen when the test is compiled using gcc 4.6.4.

Signed-off-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/vm/Makefile

@@ -7,7 +7,7 @@ BINARIES += transhuge-stress
 
 all: $(BINARIES)
 %: %.c
-	$(CC) $(CFLAGS) -o $@ $^
+	$(CC) $(CFLAGS) -o $@ $^ -lrt
 
 run_tests: all
 	@/bin/sh ./run_vmtests || (echo "vmtests: [FAIL]"; exit 1)