Fix the same problem that was fixed in rev. 1.6 and got reintroduced

in rev. 1.8 -- make btxld(8) a cross-tool for i386 and now amd64.

Tested on:	alpha (which has a different idea of __LDPGSZ)

usr.sbin/btxld/btxld.c

@@ -34,6 +34,11 @@ static const char rcsid[] =
 #include <sys/stat.h>
 #include <sys/mman.h>
 
+/* XXX make this work as an i386/amd64 cross-tool */
+#include <machine/exec.h>
+#undef __LDPGSZ
+#define __LDPGSZ	4096
+
 #include <a.out.h>
 #include <err.h>
 #include <errno.h>