Add prototype for perror()

diff --git a/include/stdio.h b/include/stdio.h
index 367e4ad..466b95c 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -95,4 +95,6 @@
 __extern int sscanf(const char *, const char *, ...);
 __extern int vsscanf(const char *, const char *, va_list);
 
+__extern void perror(const char *);
+
 #endif /* _STDIO_H */
diff --git a/klibc/include/stdio.h b/klibc/include/stdio.h
index 367e4ad..466b95c 100644
--- a/klibc/include/stdio.h
+++ b/klibc/include/stdio.h
@@ -95,4 +95,6 @@
 __extern int sscanf(const char *, const char *, ...);
 __extern int vsscanf(const char *, const char *, va_list);
 
+__extern void perror(const char *);
+
 #endif /* _STDIO_H */