cmd/compile: internal compiler error: walkExpr: switch 1 unknown op RECOVER [1.18 backport]

[gopherbot]

@ianlancetaylor requested issue #51839 to be considered for backport to the next 1.18 minor release.

@gopherbot Please open backport to 1.18

This is an internal compiler error on valid code.

[gopherbot]

Change https://go.dev/cl/394080 mentions this issue: [release-branch.go1.18] cmd/compile: fix panic with nested dead hidden closures

[toothrot]

Approved. This is a serious issue with no workaround.

[gopherbot]

Closed by merging c258e9d to release-branch.go1.18.