Revert "openssl: don't define SIXTY_FOUR_BIT_LONG on Windows"

This reverts commit 878cc3e532ec5feb7145ba0523db2c6383df748b.

Reverted for breaking the x86_64 Linux build:

    In file included from ../deps/openssl/openssl/include/openssl/bn.h:1:0,
                     from ../deps/openssl/openssl/crypto/bn/asm/../bn_lcl.h:115,
                     from ../deps/openssl/openssl/crypto/bn/asm/x86_64-gcc.c:1:
    ../deps/openssl/openssl/include/openssl/../../crypto/bn/bn.h:813:20: note: previous declaration of 'bn_add_words' was here
     BN_ULONG bn_add_words(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int num);
                        ^
    ../deps/openssl/openssl/crypto/bn/asm/x86_64-gcc.c:210:15: error: conflicting types for 'bn_sub_words'
     BN_ULONG bn_sub_words (BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,int n)

R=@piscisaureus