This reduces the number of moving parts in ABI compatibility checks.
Additionally, it also allows to use OpenSSL in FIPS mode while still
using md5 for non-security tasks.

Now we always set NGX_CC_NAME to "msvc", and additionally test compiler
version as reported by "cl" in auto/cc/msvc (the same version is also
available via the _MSC_VER define).  In particular, this approach allows
to properly check for C99 variadic macros support, which previously was
not used with MSVC versions not explicitly recognized.

Now unneeded wildcards in NGX_CC_NAME tests for msvc removed accordingly,
as well as unused wildcards for owc and icc.

instead, do chdir inside Makefile

options as --with-zlib=../zlib-1.2.3.  It seems there is no common way
to learn the current directory in Win32 make's: although nmake has MAKEDIR
variable, nevertheless Borland make's MAKEDIR is the directory where make
is installed, and OpenWatcom wmake has no MAKEDIR at all.

    *) Change: now the ngx_http_charset_module works for subrequests, if
       the response has no "Content-Type" header line.

    *) Bugfix: if the "proxy_pass" directive has no URI part, then the
       "proxy_redirect default" directive add the unnecessary slash in
       start of the rewritten redirect.

    *) Bugfix: the internal redirect always transform client's HTTP method
       to GET, now the transformation is made for the "X-Accel-Redirect"
       redirects only and if the method is not HEAD; the bug had appeared
       in 0.3.42.

    *) Bugfix: the ngx_http_perl_module could not be built, if the perl was
       built with the threads support; the bug had appeared in 0.3.46.