Make __rust_alloc_error_handler_should_panic a function
Fixesrust-lang/rust#143253
`__rust_alloc_error_handler_should_panic` is a static but was being exported as a function.
For most targets this doesn't matter, but Arm64EC Windows uses different decorations for exported variables vs functions, hence it fails to link when `-Z oom=abort` is enabled.
We've had issues in the past with statics like this (see rust-lang/rust#141061) but the tldr; is that Arm64EC needs symbols correctly exported as either a function or data, and data MUST and MUST ONLY be marked `dllimport` when the symbol is being imported from another binary, which is non-trivial to calculate for these compiler-generated statics.
So, instead, the easiest thing to do is to make `__rust_alloc_error_handler_should_panic` a function instead.
Since `__rust_alloc_error_handler_should_panic` isn't involved in any linking shenanigans, I've marked it as `AlwaysInline` with the hopes that the various backends will see that it is just returning a constant and perform the same optimizations as the previous implementation.
r? `@bjorn3`
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