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.

The change allows to compile QUIC with OpenSSL which lacks BoringSSL QUIC API.

This implementation does not support 0-RTT.

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.

The PCRE2 library is now used by default if found, instead of the
original PCRE library.  If needed for some reason, this can be disabled
with the --without-pcre2 configure option.

To make it possible to specify paths to the library and include files
via --with-cc-opt / --with-ld-opt, the library is first tested without
any additional paths and options.  If this fails, the pcre2-config script
is used.

Similarly to the original PCRE library, it is now possible to build PCRE2
from sources with nginx configure, by using the --with-pcre= option.
It automatically detects if PCRE or PCRE2 sources are provided.

Note that compiling PCRE2 10.33 and later requires inttypes.h.  When
compiling on Windows with MSVC, inttypes.h is only available starting
with MSVC 2013.  In older versions some replacement needs to be provided
("echo '#include <stdint.h>' > pcre2-10.xx/src/inttypes.h" is good enough
for MSVC 2010).

The interface on nginx side remains unchanged.

Removed ICC-specific PCRE optimizations which tried to link with PCRE
object files instead of the library.  Made compiler-specific code
minimal.

OpenSSL library QUIC support cannot be tested at configure time when
using the --with-openssl option so assume it's present if requested.
While here, fixed the error message in case QUIC support is missing.