Use internal malloc function in fips.c

* src/fips.c (check_binary_integrity): s/gcry_malloc/xtrymalloc/.
--

This fixes a build problem with ENABLE_HMAC_BINARY_CHECK.

Reported-by: Michal Vyskocil.
Support building using the latest mingw-w64 toolchain.

* acinclude.m4 (GNUPG_SYS_SYMBOL_UNDERSCORE): Change mingw detection.
--

This patch is related to Debian-bug-id 730271 for GnuPG 1.4:

   From: Stephen Kitt <skitt@debian.org>

      All MinGW targets require underscores when linking. This patch fixes
      acinclude.m4 and the resulting configure so they don't limit the use
      of underscores to the old mingw32msvc targets.

Signed-off-by: Werner Koch <wk@gnupg.org>
Comment typo fix

--
mpi: Fix a subtle bug setting spurious bits with in mpi_set_bit.

* mpi/mpi-bit.c (_gcry_mpi_set_bit, _gcry_mpi_set_highbit): Clear
allocated but not used bits before resizing.
* tests/t-mpi-bits.c (set_bit_with_resize): New.
--

Reported-by: Martin Sewelies.

This bug is probably with us for many years.  Probably due to
different memory allocation patterns, it did first revealed itself
with 1.6.  It could be the reason for other heisenbugs.

Signed-off-by: Werner Koch <wk@gnupg.org>