Fixes these errors:
```
../ext/zlib/gzlib.c:492:14: error: implicit declaration of function 'lseek' is invalid in C99
[-Werror,-Wimplicit-function-declaration]
../ext/zlib/gzwrite.c:84:15: error: implicit declaration of function 'write' is invalid in C99
[-Werror,-Wimplicit-function-declaration]
1 /* gzguts.h -- zlib internal header definitions for gz* operations
got = write(state->fd, strm->next_in, strm->avail_in);
```
Jean-André Santoni
6f2310b8ea