add MAP_FIXED_NOREPLACE from linux v4.17

to map at a fixed address without unmapping underlying mappings
(fails with EEXIST unlike MAP_FIXED), new in linux commits
4ed28639519c7bad5f518e70b3284c6e0763e650 and
a4ff8e8620d3f4f50ac4b41e8067b7d395056843.

include/sys/mman.h

@@ -35,6 +35,7 @@ extern "C" {
 #define MAP_STACK      0x20000
 #define MAP_HUGETLB    0x40000
 #define MAP_SYNC       0x80000
+#define MAP_FIXED_NOREPLACE 0x100000
 #define MAP_FILE       0
 
 #define MAP_HUGE_SHIFT 26