LibC: Add is*() functions to libc

libc/include/ctype.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+int isalnum(int);
+int isalpha(int);
+int isascii(int);
+int isblank(int);
+int iscntrl(int);
+int isdigit(int);
+int isgraph(int);
+int islower(int);
+int isprint(int);
+int ispunct(int);
+int isspace(int);
+int isupper(int);
+int isxdigit(int);
+
+__END_DECLS