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>