cmd/compile: prefer base.Fatalf to panic in dwarfgen

[derekparker]

Updates a few spots which call panic to instead call base.Fatalf.

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Derek Parker:

Patch Set 1:

(1 comment)

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Message from Keith Randall:

Patch Set 1: Code-Review+2 Commit-Queue+1

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Message from Go LUCI:

Patch Set 1:

Dry run: CV is trying the patch.

Bot data: {"action":"start","triggered_at":"2025-07-15T15:37:52Z","revision":"83239b5e1d0a7797bbdf1dadf46b9c27433c6987"}

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Message from Keith Randall:

Patch Set 1: Code-Review+1

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Message from Keith Randall:

Patch Set 1: -Commit-Queue

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Patch Set 1:

This CL has passed the run

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Message from Go LUCI:

Patch Set 1: LUCI-TryBot-Result+1

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This PR is being closed because golang.org/cl/688035 has been merged.