Add prototypes for mkstemp replacements.

Should prevent warnings due to our wrapper function.

openbsd-compat/mktemp.c

@@ -37,6 +37,7 @@
 #ifdef mkstemp
 #undef mkstemp
 #endif
+int mkstemp(char *);
 
 /*
  * From glibc man page: 'In glibc versions 2.06 and earlier, the file is

openbsd-compat/openbsd-compat.h

@@ -142,6 +142,7 @@ char *mkdtemp(char *path);
 #endif
 
 #define mkstemp(x) _ssh_mkstemp(x)
+int _ssh_mkstemp(char *);
 
 #ifndef HAVE_DAEMON
 int daemon(int nochdir, int noclose);