Audit the LFS functions from Linux and add the same for Android if
bionic supports it, according to libc.map from API 23 (Android 6.0).

The standard library is currently limited to API 18, so it may only use
`lseek64`, `pread64`, `pwrite64`, `ftruncate64`, and `readahead`.

Note that `stat64` and `dirent64` are actually identical to the regular
versions, because bionic has always mapped them to the LFS syscalls.
It also sets `O_LARGEFILE` at all times, so `open` matches `open64`.
Still, the explicit LFS names may be useful to match Linux.

Fixes #189.