[PATCH] osdep/mmap.h: define MAP_FAILED if necessary

If sys/mman.h defines MAP_FAILED, config.h will not define MAP_FAILED.
In this case, MAP_FAILED is not defined at all and compilation errors
occur.
---
 osdep/mmap.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/osdep/mmap.h b/osdep/mmap.h
index db7c136a9..9bd1b9e4b 100644
--- a/osdep/mmap.h
+++ b/osdep/mmap.h
@@ -46,7 +46,9 @@
  */
 #define MAP_ANON    0x1000  /* allocated from memory, swap space */
 
-/* MAP_FAILED is defined in config.h */
+#ifndef MAP_FAILED
+#define MAP_FAILED  ((void *) -1)
+#endif
 
 #ifndef _MMAP_DECLARED
 #define _MMAP_DECLARED
-- 
2.42.0