os: Check for EINTR on ftruncate()

The man page indicates that ftruncate() can set errno to EINTR, so test
for this.

I have not actually been able to provoke an EINTR error from ftruncate()
in testing though.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>

shared/os-compatibility.c

@@ -187,7 +187,9 @@ os_create_anonymous_file(off_t size)
 		return -1;
 	}
 #else
+	do {
 		ret = ftruncate(fd, size);
+	} while (ret < 0 && errno == EINTR);
 	if (ret < 0) {
 		close(fd);
 		return -1;