MREMAP is unimplemented on GNU/Hurd for now

--- a/bits/mman.h
+++ b/bits/mman.h
@@ -85,10 +85,12 @@
 #define MS_INVALIDATE	2		/* Invalidate the caches.  */
 
 /* Flags for `mremap'.  */
+#if 0
 #ifdef __USE_GNU
 # define MREMAP_MAYMOVE	1		/* Mapping address may change.  */
 # define MREMAP_FIXED	2		/* Fifth argument sets new address.  */
 #endif
+#endif
 
 /* Flags for `mlockall' (can be OR'd together).  */
 #define MCL_CURRENT	1		/* Lock all currently mapped pages.  */
--- a/malloc/memusage.c
+++ b/malloc/memusage.c
@@ -680,6 +680,9 @@ mmap64 (void *start, size_t len, int pro
   return result;
 }
 
+#ifndef MREMAP_FIXED
+#define MREMAP_FIXED 0
+#endif
 
 /* `mremap' replacement.  We do not have to keep track of the size since
    `munmap' will get it as a parameter.  */