Libraries should be listed last on the compiler's command line, so that
the linker can look for and find still unresolved symbols. The librt
library, required for the shm_* functions, was announced using CFLAGS,
which puts the library *before* the source files, and fails compilation
on my system:
======================
gcc -isystem /src/linux-selftests/usr/include -Wall -lrt test_cachestat.c
  -o /src/linux-selftests/kselftest/cachestat/test_cachestat
/usr/bin/ld: /tmp/cceQWO3u.o: in function `test_cachestat_shmem':
test_cachestat.c:(.text+0x890): undefined reference to `shm_open'
/usr/bin/ld: test_cachestat.c:(.text+0x99c): undefined reference to `shm_unlink'
collect2: error: ld returned 1 exit status
make[4]: *** [../lib.mk:181: /src/linux-selftests/kselftest/cachestat/test_cachestat] Error 1
======================

Announce the library using the LDLIBS variable, which ensures the proper
ordering on the command line.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>