To ensure proper target selection the NGX_MACHINE variable is now set
based on the MSVC compiler output, and the OpenSSL target is set based
on it.

This is not important as long as "no-asm" is used (as in misc/GNUmakefile
and win32 build instructions), but might be beneficial if someone is trying
to build OpenSSL with assembler code.

Threads are disabled during UNIX builds (see b329c0ab1a48), and also not
needed for Windows builds.

This used to be the default before OpenSSL 1.1.0.

OpenSSL 1.1.0 now uses normal "nmake; nmake install" instead of using
custom "ms\do_ms.bat" script and "ms\nt.mak" makefile.  And Configure
now requires --prefix to be absolute, and no longer derives --openssldir
from prefix (so it's specified explicitly).  Generated libraries are now
called "libcrypto.lib" and "libssl.lib" instead of "libeay32.lib"
and "ssleay32.lib".  Appropriate tests added to support both old and new
variants.

Additionally, openssl/lhash.h now triggers warning C4090 ('function' :
different 'const' qualifiers), so the warning was disabled.