ctype: Implement _tolower, _toupper

include/bits/ctype.h

+#ifndef _BITS_CTYPE_H
+#define _BITS_CTYPE_H
+
+#define _tolower(c) tolower(c)
+#define _toupper(c) toupper(c)
+
+#endif /* _BITS_CTYPE_H */

src/header/ctype/cbindgen.toml

-sys_includes = []
+sys_includes = ["bits/ctype.h"]
 include_guard = "_CTYPE_H"
 language = "C"
 style = "Tag"