xdiff: fix builds on Windows

This works on my ancient Fedora system too, without warnings.  There are,
however, warnings about various 64 to 32 bit conversions on Windows that need to
be examined.

mercurial/thirdparty/xdiff/xdiffi.c

@@ -30,6 +30,10 b''
 #define XDL_SNAKE_CNT 20
 #define XDL_K_HEUR 4
 
+/* VC 2008 doesn't know about the inline keyword. */
+#if defined(_MSC_VER)
+#define inline __forceinline
+#endif
 
 
 typedef struct s_xdpsplit {

mercurial/thirdparty/xdiff/xinclude.h

@@ -26,7 +26,6 b''
 #include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <unistd.h>
 #include <string.h>
 #include <limits.h>