Add strchr() and putchar() to local C library

Change-Id: I3659e119a242f8ef828e32bfdf5d0b4b7ac4f716
diff --git a/include/stdlib/string.h b/include/stdlib/string.h
index 12b1000..832d764 100644
--- a/include/stdlib/string.h
+++ b/include/stdlib/string.h
@@ -55,6 +55,7 @@
 void	*memmove(void *, const void *, size_t);
 void	*memset(void *, int, size_t);
 
+char	*strchr(const char *, int) __pure;
 size_t	 strlen(const char *) __pure;
 
 __END_DECLS