Cherry-picking the following changes that fixes zlib, jemalloc and gflags dependencies, and fixes a flaky test:
```
6ead62ca 2019-07-25 yiwu@pingcap.com     Avoid build require system zlib (#303)
9246b9c5 2019-07-25 hi@breeswish.org     Skip jemalloc options on specific platform (#324)
7a8dd731 2019-07-22 yiwu@pingcap.com     Add jemalloc-sys dependency when jemalloc is enabled (#320)
6f2c6320 2019-07-23 yiwu@pingcap.com     Not compile with gflags (#322)
09b80321 2019-07-22 yiwu@pingcap.com     Fix perf context test (#321)
d67f38e2 2019-07-21 yiwu@pingcap.com     Add jemalloc feature (#319)
```

Also update rocksdb to fix compile error with gcc9:
```
7a03c83ed 2019-07-23 psergey@askmonty.org Fix MyRocks compile warnings-treated-as-errors on Fedora 30, gcc 9.1.1 (#5553)
```