move MREMAP_MAYMOVE and MREMAP_FIXED out of bits

the definitions are generic for all kernel archs. exposure of these
macros now only occurs on the same feature test as for the function
accepting them, which is believed to be more correct.

include/sys/mman.h

@@ -32,6 +32,8 @@ int mlockall (int);
 int munlockall (void);
 
 #ifdef _GNU_SOURCE
+#define MREMAP_MAYMOVE 1
+#define MREMAP_FIXED 2
 void *mremap (void *, size_t, size_t, int, ...);
 int remap_file_pages (void *, size_t, int, size_t, int);
 #endif