MinGW: disable self-contained mode when cross compiling

[mati865]

When cross compiling users have to provide own linker and libraries anyway.
Using rust provided MinGW crt objects is harmful here and has no benefits.

cc #68887

[rust-highfive]

r? @matthewjasper

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[JohnTitor]

This hasn't got any response for about three weeks, let's re-assign following GitHub recommendation.
r? @petrochenkov

[petrochenkov]

When cross compiling users have to provide own linker and libraries anyway.

If we are cross-compiling from Windows (MSVC, or Mingw with different bit-ness) then the Rust-provided linker should work as well?
I'm all for limiting the self-contained mode, but we may have to partially revert this later if the aforementioned scenarios are used in practice.
@bors r+

[bors]

📌 Commit 08990e5 has been approved by petrochenkov

[bors]

💡 This pull request was already approved, no need to approve it again.

• There's another pull request that is currently being tested, blocking this pull request: [beta] Make ClashingExternDeclarations Allow by default. #74966

[bors]

📌 Commit 08990e5 has been approved by petrochenkov

[mati865]

If we are cross-compiling from Windows (MSVC, or Mingw with different bit-ness) then the Rust-provided linker should work as well?

In that case rust-mingw is not installed so Rust doesn't provide the linker.

[bors]

⌛ Testing commit 08990e5 with merge 568f619...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: petrochenkov
Pushing 568f619 to master...