MSVC regression-test job in CI now uses -include-std to workaround a problem with support for C++ modules

[bluetarpmedia]

Fixes (or works around) #943

Note that this fix has exposed some MSVC pure2 tests which were silently failing:

• pure2-main-args.cpp.execution
• pure2-repeated-call.cpp.execution
• pure2-union.cpp.execution
• pure2-variadics.cpp.execution

I updated all of them except pure2-main-args.cpp.execution since I wasn't sure what the correct result should be. The diff from the GitHub agent run is:

-args.argv[0]         is test.exe
+args.argv[0]         is D:\cppfront\cppfront

[hsutter]

Thanks!