Win32: simplified and improved handling of MSVC versions.

Win32: simplified and improved handling of MSVC versions.

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.