Corrected spelling mistakes in comments and strings

include/stddef.h

@@ -31,7 +31,7 @@ void *alloca(size_t size);
    by __need_wint_t, as otherwise stddef.h isn't allowed to
    define this type).   Note that this must be outside the normal
    _STDDEF_H guard, so that it works even when we've included the file
-   already (without requring wint_t).  Some other libs define _WINT_T
+   already (without requiring wint_t).  Some other libs define _WINT_T
    if they've already provided that type, so we can use that as guard.
    TCC defines __WINT_TYPE__ for us.  */
 #if defined (__need_wint_t)