Fix building with x86-64 medium and large memory models

Fix building with x86-64 medium and large memory models

* cipher/cast5-amd64.S [HAVE_COMPATIBLE_GCC_WIN64_PLATFORM_AS]
(GET_EXTERN_POINTER): Load 64-bit address instead of 32-bit.
* cipher/rijndael.c (do_encrypt, do_decrypt)
[USE_AMD64_ASM && !HAVE_COMPATIBLE_GCC_AMD64_PLATFORM_AS]: Load
table pointer through register instead of generic reference.
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Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>