util/os_file: dont assign cloexec when previously assigned

The EGL_MESA_platform_gbm example code placed inside the EGL reg
can crash in nouveau as gbm_create_device is passed with a fd
that already has FD_CLOEXEC and nouveau attempts to add FD_CLOEXEC
to everything passed to it which just leads to nouveau using a bad
fd. Check to make sure cloexec is not assigned before assiging it
when duplicating fds with the flag.

Signed-off-by: Yusuf Khan <yusisamerican@gmail.com>

src/util/os_file.c

@@ -51,6 +51,10 @@ int
 os_dupfd_cloexec(int fd)
 {
    int minfd = 3;
+
+   if (fcntl(fd, F_GETFL) & FD_CLOEXEC)
+      return dup(fd);
+
    int newfd = fcntl(fd, F_DUPFD_CLOEXEC, minfd);
 
    if (newfd >= 0)