Fix no_integrated_as option to work with new codegen architecture.

[pftbest]

Old implementation called the assembler once per crate, but we need to call
it for each object file instead, because a single crate can now have more
than one object file.

This patch fixes #45836 (Can't compile core for msp430 in release mode)

This change can be tested on x86_64 using

export RUSTFLAGS="-C no_integrated_as -C save_temps"

r? @alexcrichton
cc @japaric

[rust-highfive]

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[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit 3f61742 has been approved by alexcrichton

[nagisa]

This change can be tested on x86_64 using

export RUSTFLAGS="-C no_integrated_as -C save_temps"

Is it possible to add a make-run test that tests this, then?

[pftbest]

@nagisa I've added the test, but it's primitive.

[alexcrichton]

@bors: r+

[bors]

📌 Commit 98dee04 has been approved by alexcrichton

[bors]

☔ The latest upstream changes (presumably #47748) made this pull request unmergeable. Please resolve the merge conflicts.