This patch enables correct compilation on both MacOS and Linux using only
POSIX.1-2008-compliant C with XSI extensions.
Specifically, POSIX.1-2008 is the minimum version because we use strdup(3);
explicit XSI is required to expose putenv from glibc.
It shares the create/open/delete/set_version/get_file_size
functions with POSIX backend.
The mmap backend also supports fsync and fsyncPerWrite options,
and it will use msync() instead and fsync().
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Glenn K. Lockwood