perf build: Add libbabeltrace to build-test

'make build-test' doesn't test LIBBABELTRACE=1. It misses a building
failure caused by commit 41840d21 ("perf config: Move config
declarations from util/cache.h to util/config.h"), breaks bisect.

Add LIBBABELTRACE=1 to build-test.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1466818918-131281-1-git-send-email-wangnan0@huawei.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>