fix recursive named pointer types

[cpunion]

Summary

• avoid eager LLVM element type expansion for opaque pointers
• cover recursive and mutually recursive named type literals in test/go
• remove the goroot xfail for fixedbugs/bug336.go

Verification

• go test ./test/go -count=1
• LLGO_ROOT="/Users/lijie/source/goplus/llgo-wt-goroot-fixedbugs-recursive-types" /tmp/llgo-recursive-types-fixed test ./test/go -run TestRecursiveNamedTypeLiterals -count=1
• go test ./test/goroot -run TestGoRootRunCases -count=1 -timeout 30m -args -goroot "/opt/homebrew/Cellar/go@1.24/1.24.11/libexec" -dirs fixedbugs -case '^fixedbugs/bug336.go$' -xfail /tmp/llgo-empty-xfail-does-not-exist.yaml -run-timeout 2m -build-timeout 5m
• go test ./ssa -count=1
• go test ./ssa -run TestPointerTypeDoesNotExpandRecursiveNamedElement -count=1
• go test ./cl -run '^TestRunAndTestFromTestgo$/^typerecur$' -count=1

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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