The test in test/strmode.c can fail to compile depending on the
optimization flags used.
The constants that are used in this file (S_IFREG etc.) come from the
<sys/stat.h> include file. It seems gcc ignores this error if one
compiles with "-O2" (default), but if one uses no optimization it fails.
Add the missing include and it works all the time.
Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=93880
Signed-off-by: Guillem Jover <guillem@hadrons.org>
