Auto merge of #99553 - ChrisDenton:lazy-compat-fn, r=Mark-Simulacrum

Auto merge of #99553 - ChrisDenton:lazy-compat-fn, r=Mark-Simulacrum

Rewrite Windows `compat_fn` macro

This allows using most delay loaded functions before the init code initializes them. It also only preloads a select few functions, rather than all functions.

This is optimized for the common case where a function is used after already being loaded (or failed to load). The only change in codegen at the call site is to use an atomic load instead of a plain load, which should have negligible or no impact.

I've split the old `compat_fn` macro in two so as not to mix two different use cases. If/when Windows 7 support is dropped `compat_fn_optional` can be removed entirely.

r? rust-lang/libs