SHA-1: Add SSSE3 implementation

* cipher/Makefile.am: Add 'sha1-ssse3-amd64.c'.
* cipher/sha1-ssse3-amd64.c: New.
* cipher/sha1.c (USE_SSSE3): New.
(SHA1_CONTEXT) [USE_SSSE3]: Add 'use_ssse3'.
(sha1_init) [USE_SSSE3]: Initialize 'use_ssse3'.
(transform): Rename to...
(_transform): this.
(transform): New.
* configure.ac [host=x86_64]: Add 'sha1-ssse3-amd64.lo'.

Patch adds SSSE3 implementation based on white paper "Improving the Performance
of the Secure Hash Algorithm (SHA-1)" at
http://software.intel.com/en-us/articles/improving-the-performance-of-the-secure-hash-algorithm-1

Benchmarks:

cpu Old New Diff
Intel i5-4570 9.02 c/B 5.22 c/B 1.72x
Intel i5-2450M 12.27 c/B 7.24 c/B 1.69x
Intel Core2 T8100 7.94 c/B 6.76 c/B 1.17x

• Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>