ctype: align size of category bit fields to small targets needs

E.g. arm ABI requires -fshort-enums for bare-metal toolchains.
Given there are only 29 category enums, the compiler chooses an
8 bit enum type, so a size of 11 bits for the bitfield leads to
a compile time error:

  error: width of 'cat' exceeds its type
    enum category cat: 11;
                  ^~~

Fix this by aligning the size of the category members to byte
borders.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

newlib/libc/ctype/categories.c

@@ -2,8 +2,8 @@
 #include "categories.h"
 
 struct _category {
-  enum category cat: 11;
-  unsigned int first: 21;
+  enum category cat: 8;
+  unsigned int first: 24;
   unsigned short delta;
 } __attribute__((packed));