importproject: fix reading of msvc std option

[ludviggunne]

Might need more tests. The fix is a bit hacky but I thought I'd make as small of a change as possible.

[firewave]

Will take a look later. That also lacks support for c++latest and clatest: https://learn.microsoft.com/en-us/cpp/build/reference/std-specify-language-standard-version?view=msvc-170.

The note about __cplusplus is also interesting. And it also has _MSVC_LANG as equivalent. Stupid quirks...

[ludviggunne]

The note about __cplusplus is also interesting. And it also has _MSVC_LANG as equivalent. Stupid quirks...

The __cplusplus thing is quirky indeed... atleast with this change the correct substring is extracted from the command.

[firewave]

I will take a look after I finished up #6742 but that still requires some work as it exposes additional issues. So give it a day or two (or a week or two depending on how the reviews progress if they intersect).