wrapper: move xmmap() to sha1_file.c

wrapper.o depends on sha1_file.o for a number of reasons.  One is
release_pack_memory().

xmmap function calls mmap, discarding unused pack windows when
necessary to relieve memory pressure.  Simple git programs using
wrapper.o as a friendly libc do not need this functionality.
So move xmmap to sha1_file.o, where release_pack_memory() is.
Signed-off-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

sha1_file.c

@@ -576,6 +576,21 @@ void release_pack_memory(size_t need, int fd)
 		; /* nothing */
 }
 
+void *xmmap(void *start, size_t length,
+	int prot, int flags, int fd, off_t offset)
+{
+	void *ret = mmap(start, length, prot, flags, fd, offset);
+	if (ret == MAP_FAILED) {
+		if (!length)
+			return NULL;
+		release_pack_memory(length, fd);
+		ret = mmap(start, length, prot, flags, fd, offset);
+		if (ret == MAP_FAILED)
+			die_errno("Out of memory? mmap failed");
+	}
+	return ret;
+}
+
 void close_pack_windows(struct packed_git *p)
 {
 	while (p->windows) {

wrapper.c

@@ -108,21 +108,6 @@ void *xcalloc(size_t nmemb, size_t size)
 	return ret;
 }
 
-void *xmmap(void *start, size_t length,
-	int prot, int flags, int fd, off_t offset)
-{
-	void *ret = mmap(start, length, prot, flags, fd, offset);
-	if (ret == MAP_FAILED) {
-		if (!length)
-			return NULL;
-		release_pack_memory(length, fd);
-		ret = mmap(start, length, prot, flags, fd, offset);
-		if (ret == MAP_FAILED)
-			die_errno("Out of memory? mmap failed");
-	}
-	return ret;
-}
-
 /*
  * xread() is the same a read(), but it automatically restarts read()
  * operations with a recoverable error (EAGAIN and EINTR). xread()