Revert "coverage: Enlarge empty spans during MIR instrumentation, not codegen"
Surprisingly, rust-lang/rust#144298 alone (extracted from rust-lang/rust#140847) was enough to re-trigger the failures observed in https://github.com/rust-lang/rust/issues/141577#issuecomment-3120667286.
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This reverts commit f877aa7d14.
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r? ghost
The codegen crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.