[win] Ignore MSVC linker warning 4217

[dpaoliello]

Fixes a regression from #140176

As part of fixing linking statics for Arm64EC, we needed to correctly mark statics with the DATA attribute in the generated def file.

A side-effect of this is that statics that need to be imported must be marked with dllimport.

This then caused issues with __rust_no_alloc_shim_is_unstable as it is marked extern "Rust" in the static library (indicating that it is a foreign item, thus it is linked into the binary), but the definition is generated by the compiler (in some crates). MSVC's linker would raise warning 4286 to complain about marking a symbol as dllimport that is defined in an obj file, but LLD is raising warning 4217 to complain that the symbol is declared in one obj but imported by another (it's possible the difference is due to the number of codegen-units and where the definition/declarations happen to land across the objs).

The fix here is to suppress warning 4217 as well.

Long term, it would be ideal to avoid marking __rust_no_alloc_shim_is_unstable as dllimport if we know that the compiler will be generating it in the current crate.

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[rustbot]

These commits modify compiler targets.
(See the Target Tier Policy.)

[dpaoliello]

cc @zmodem

[jieyouxu]

r? @bjorn3