CI: fix travis build with clang

With this patch, Travis will build/test CRIU using clang, for real.

I swear I fixed it before, but the fix was apparently lost.

travis-ci: success for series starting with [1/3] compel: mv noexecstack from CFLAGS to LDFLAGS
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

scripts/travis/travis-tests

@@ -27,8 +27,8 @@ ulimit -c unlimited
 echo "|`pwd`/test/abrt.sh %P %p %s %e" > /proc/sys/kernel/core_pattern
 
 export GCOV
-make $(MAKE_VARS)
-make $(MAKE_VARS) -C test/zdtm
+make ${MAKE_VARS}
+make ${MAKE_VARS} -C test/zdtm
 
 ./criu/criu check
 ./criu/criu check --all || echo $?