Fix some warnings.

compat/forkpty-aix.c

@@ -25,6 +25,9 @@
 
 #include "compat.h"
 
+void fatal(const char *, ...);
+void fatalx(const char *, ...);
+
 pid_t
 forkpty(int *master, unused char *name, struct termios *tio, struct winsize *ws)
 {

compat/forkpty-hpux.c

@@ -24,6 +24,9 @@
 
 #include "compat.h"
 
+void fatal(const char *, ...);
+void fatalx(const char *, ...);
+
 pid_t
 forkpty(int *master, char *name, struct termios *tio, struct winsize *ws)
 {

compat/forkpty-sunos.c

@@ -26,6 +26,9 @@
 
 #include "compat.h"
 
+void fatal(const char *, ...);
+void fatalx(const char *, ...);
+
 pid_t
 forkpty(int *master, char *name, struct termios *tio, struct winsize *ws)
 {

compat/strcasestr.c

@@ -36,6 +36,8 @@
 #include <ctype.h>
 #include <string.h>
 
+#include "compat.h"
+
 /*
  * Find the first occurrence of find in s, ignore case.
  */

compat/strsep.c

@@ -32,6 +32,8 @@
 #include <string.h>
 #include <stdio.h>
 
+#include "compat.h"
+
 /*
  * Get next token from string *stringp, where tokens are possibly-empty
  * strings separated by characters from delim.