Support EII on Windows MSVC

[AsakuraMizu]

Tracking issue: #125418

The previous PR #158294 made function EIIs work on Windows MSVC. This PR fixes support for static EIIs, enabling full EII support on Windows MSVC.

The following fixes are included:

• Keep EII statics out of LLVM internalization
• Mark EII static symbols as dllimport
• Emit MSVC __imp_<symbol> stubs for aliases to static data

Note: LLVMAddAlias2 was incorrectly declared in the llvm-wrapper extern block previously.

[rustbot]

r? @adwinwhite

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[adwinwhite]

@rustbot reroll

[bjorn3]

If you change this to a .map().filter() the filter code should be almost identical to the filter code of iter_globals, which may be a bit easier to understand. You could also try if something like the following would work:

iter::chain(
    base::iter_globals(llmod),
    base::iter_global_aliases(llmod)
        .filter(|&val| llvm::LLVMGetTypeKind(unsafe { llvm::LLVMGlobalGetValueType(val) }).to_rust() != llvm::TypeKind::Function)
)
    .map(|val| (val, llvm::get_linkage(val))
    .filter(|(val, linkage)| matches!(linkage, llvm::Linkage::ExternalLinkage | llvm::Linkage::WeakAnyLinkage) && !llvm::is_declaration(val))

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