Summary:
The compiler flag `-DROCKSDB_FALLOCATE_PRESENT` was only set when
`fallocate`, `FALLOC_FL_KEEP_SIZE`, and `FALLOC_FL_PUNCH_HOLE` were all
present. However, the last of the three is not really necessary for the
primary `fallocate` use case; furthermore, it was introduced only in later
Linux kernel versions (2.6.38+).

This PR changes the flag `-DROCKSDB_FALLOCATE_PRESENT` to only require
`fallocate` and `FALLOC_FL_KEEP_SIZE` to be present. There is a separate
check for `FALLOC_FL_PUNCH_HOLE` only in the place where it is used.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5023

Differential Revision: D14248487

Pulled By: siying

fbshipit-source-id: a10ed0b902fa755988e957bd2dcec9081ec0502e