Bug 1020590 - Fix ASAN builds after bug 1013341. r=mshal
Bug 965870 - Try to use __builtin_ffsl if ffsl is unavailable. r=mshal

Cherry-picked from https://github.com/jemalloc/jemalloc/commit/9c3a10fdf6baa5ddb042b6adbef1ff1b3c613ce3
Bug 965870 - Check for __builtin_ffsl before ffsl. r=mshal

Cherry-picked from https://github.com/jemalloc/jemalloc/commit/1a3eafd1b045163f27e4a5acf01280edfe28c309