Allow compile-time specification that small code space is desired

Allow compile-time specification that small code space is desired

* d3_cbc.c (krb5int_des3_cbc_encrypt, krb5int_des3_cbc_decrypt): Don't declare
left and right variables as registers.
* f_cksum.c (mit_des_cbc_cksum): Likewise.
* f_cbc.c (krb5int_des_cbc_encrypt, krb5int_des_cbc_decrypt): Likewise.
(krb5int_des_cbc_encrypt): For full blocks, use GET_HALF_BLOCK to read and then
xor, instead of processing each byte individually.
(krb5int_des_do_encrypt_2, krb5int_des_do_decrypt_2) [CONFIG_SMALL]: New
functions, wrapping large macros with the DES inner loops.
* f_tables.h (DES_DO_ENCRYPT_1, DES_DO_DECRYPT_1): Renamed from non-_1 names.
(krb5int_des_do_encrypt_2, krb5int_des_do_decrypt_2): Declare if CONFIG_SMALL
is defined.
(DES_DO_ENCRYPT, DES_DO_DECRYPT): Expand to _1 macros or _2 function calls
depending on whether CONFIG_SMALL is defined.

With CONFIG_SMALL defined, on x86/gcc/glibc, this drops about 5K (25%) of the
code/table space.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@17183 dc483132-0cff-0310-8789-dd5450dbe970