Handle old Linux/(G)LIBC and UNIX systems the same

Linux systems pre Linux 3.11, and UNIX do not have the O_TMPFILE flag,
so let's treat them the same, by wrapping tmpfile().

Signed-off-by: David Brownlee <abs@absd.org>
Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

tempfile.c

@@ -17,17 +17,9 @@
 
 #include <paths.h>
 #include <fcntl.h>		/* O_TMPFILE requires -D_GNU_SOURCE */
-#include <linux/version.h>
-#include <stdlib.h>		/* mkstemp() */
 #include <stdio.h>		/* fdopen() */
 #include <sys/stat.h>		/* umask() */
 
-#ifndef  O_TMPFILE		/* Too old GLIBC or kernel */
-#warning O_TMPFILE missing on your system, tempfile() may not work!
-#define  __O_TMPFILE 020000000
-#define  O_TMPFILE (__O_TMPFILE | O_DIRECTORY) /* Define and let it fail at runtime */
-#endif
-
 /**
  * tempfile - A secure tmpfile() replacement
  *
@@ -43,7 +35,7 @@
  */
 FILE *tempfile(void)
 {
-#if LINUX_VERSION_CODE >= KERNEL_VERSION(3,11,0)
+#ifdef O_TMPFILE	  /* Only on Linux, with fairly recent (G)LIBC */
 	int fd;
 	mode_t oldmask;
 
@@ -55,8 +47,7 @@ FILE *tempfile(void)
 
 	return fdopen(fd, "rw");
 #else
-#warning Too old kernel, reverting to wrap unsafe tmpfile() ...
-	return tmpfile();
+	return tmpfile(); /* Fallback on older GLIBC/Linux and actual UNIX systems */
 #endif
 }