Add check for __clang__ in lone _MSC_VER checks

[nashiora]

The nob_cc_flags and nob_cc_output macros check for _MSC_VER to provide MSVC-specific argument syntax. When using Clang on Windows it provides many of the same flags as MSVC, presumably for Windows compat, so Nob was generating MSVC flags for a Clang compiler call.

This is not an issue in other locations as __clang__ is checked for explicitly and before _MSC_VER, such as in the related nob_cc macro for selecting the appropriate compiler program name.

[nashiora]

Yes I know these are trivial to re-define on your own, but IMO the default behavior should be correct.