[windows-gnu]: allow dynamic crt use

[ognevny]

windows-gnullvm has support of dynamic crt which is controlled by crt-static target feature

after 1.85.0 update in msys2 crt-static is forced to true (while it's still controllable by RUSTFLAGS though) to prevent confusions as gnullvm compiler can link libunwind.dll dynamically

edit: fixed typo

[bjorn3]

Are you talking about the -gnu target (as the issue title says) or about the -gnullvm target?

after 1.85.0 update in msys2 crt-static is forced to false

That diff makes it true, not false.

[ognevny]

Are you talking about the -gnu target (as the issue title says) or about the -gnullvm target?

-gnu

That diff makes it true, not false.

sorry, my mistake. of course I meant true :)

[ognevny]

Are you talking about the -gnu target (as the issue title says) or about the -gnullvm target?

-gnu

I meant that for -gnu the behaviour should be the same as for -gnullvm

[bjorn3]

I suspect the reason the windows-gnu target uses crt-static is because otherwise people would have to ship a copy of mingw with their app by default. The windows-gnullvm target however depends on the ucrt as libc implementation, which is available on all supported windows versions.

[ognevny]

I suspect the reason the windows-gnu target uses crt-static is because otherwise people would have to ship a copy of mingw with their app by default. The windows-gnullvm target however depends on the ucrt as libc implementation, which is available on all supported windows versions.

for windows-gnullvm crt-static changes only libunwind linkage. current default is linking libunwind.dll over libunwind.a. theoretically the same can be implemented with windows-gnu with some of gcc libraries

edit: windows-gnu also uses some windows libraries (it can use either msvcrt or ucrt)

[ognevny]

forgot to mention @mati865. he can correct me in case me said something wrong...

[mati865]

That's correct.
Windows-gnu links the unwinder library statically if the resulting executable doesn't depend on shared libraries. It doesn't allow changing this behavior without using custom target JSON.
Windows-gnullvm now links the shared library for the unwinder but can be overridden using crt-static.

These two target families shouldn't differ in this regard, so ideally, they would use windows-gnu behaviour of choosing the library. And also be overridable with crt-static.