SHA-512: Add AVX and AVX2 implementations for x86-64

* cipher/Makefile.am: Add 'sha512-avx-amd64.S' and
'sha512-avx2-bmi2-amd64.S'.
* cipher/sha512-avx-amd64.S: New.
* cipher/sha512-avx2-bmi2-amd64.S: New.
* cipher/sha512.c (USE_AVX, USE_AVX2): New.
(SHA512_CONTEXT) [USE_AVX]: Add 'use_avx'.
(SHA512_CONTEXT) [USE_AVX2]: Add 'use_avx2'.
(sha512_init, sha384_init) [USE_AVX]: Initialize 'use_avx'.
(sha512_init, sha384_init) [USE_AVX2]: Initialize 'use_avx2'.
[USE_AVX] (_gcry_sha512_transform_amd64_avx): New.
[USE_AVX2] (_gcry_sha512_transform_amd64_avx2): New.
(transform) [USE_AVX2]: Add call for AVX2 implementation.
(transform) [USE_AVX]: Add call for AVX implementation.
* configure.ac (HAVE_GCC_INLINE_ASM_BMI2): New check.
(sha512): Add 'sha512-avx-amd64.lo' and 'sha512-avx2-bmi2-amd64.lo'.
* doc/gcrypt.texi: Document 'intel-cpu' and 'intel-bmi2'.
* src/g10lib.h (HWF_INTEL_CPU, HWF_INTEL_BMI2): New.
* src/hwfeatures.c (hwflist): Add "intel-cpu" and "intel-bmi2".
* src/hwf-x86.c (detect_x86_gnuc): Check for HWF_INTEL_CPU and
HWF_INTEL_BMI2.
--

Patch adds fast AVX and AVX2 implementation of SHA-512 by Intel Corporation.
The assembly source is licensed under 3-clause BSD license, thus compatible
with LGPL2.1+. Original source can be accessed at:
 http://www.intel.com/p/en_US/embedded/hwsw/technology/packet-processing#docs

Implementation is described in white paper
 "Fast SHA512 Implementations on Intel® Architecture Processors"
 http://www.intel.com/content/www/us/en/intelligent-systems/intel-technology/fast-sha512-implementat$

Note: AVX implementation uses SHLD instruction to emulate RORQ, since it's
      faster on Intel Sandy-Bridge. However, on non-Intel CPUs SHLD is much
      slower than RORQ, so therefore AVX implementation is (for now) limited
      to Intel CPUs.
Note: AVX2 implementation also uses BMI2 instruction rorx, thus additional
      HWF flag.

Benchmarks:

cpu                 Old         SSSE3       AVX/AVX2   Old vs AVX/AVX2
                                                              vs SSSE3
Intel i5-4570       10.11 c/B    7.56 c/B   6.72 c/B   1.50x  1.12x
Intel i5-2450M      14.11 c/B   10.53 c/B   8.88 c/B   1.58x  1.18x

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Fix W32 build

* random/rndw32.c (register_poll, slow_gatherer): Change gcry_xmalloc to
xmalloc, and gcry_xrealloc to xrealloc.
--

Patch fixes following errors:

../random/.libs/librandom.a(rndw32.o): In function `registry_poll':
.../libgcrypt/random/rndw32.c:434: undefined reference to `__gcry_USE_THE_UNDERSCORED_FUNCTION'
.../libgcrypt/random/rndw32.c:454: undefined reference to `__gcry_USE_THE_UNDERSCORED_FUNCTION'
../random/.libs/librandom.a(rndw32.o): In function `slow_gatherer':
.../random/rndw32.c:658: undefined reference to `__gcry_USE_THE_UNDERSCORED_FUNCTION'

Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Fix empty clobber in AVX2 assembly check

* configure.ac (gcry_cv_gcc_inline_asm_avx2): Add "cc" as assembly
globber.
--

Appearently empty globbers only work in some cases on linux, and fail on
mingw32.

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