Fix rndhw for 64-bit Windows build

* configure.ac: Add sizeof check for 'void *'.
* random/rndhw.c (poll_padlock): Check for SIZEOF_VOID_P == 8
instead of defined(__LP64__).
(RDRAND_LONG): Check for SIZEOF_UNSIGNED_LONG == 8 instead of
defined(__LP64__).

LP64 is not predefined for 64-bit mingw64-gcc, which caused wrong
assembly code selections. Do selection based on type sizes instead,
to support x86_64, x32 and win64 properly.

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