fix panic for nil value method wrappers

[cpunion]

Fixes the remaining fixedbugs/issue19040.go panic text mismatch by implementing the compiler-generated wrapnilchk path for value-method wrappers invoked through nil pointers.

Coverage:

• Adds test/go coverage for nil *T assigned to an interface and calling a value receiver method.
• Removes the fixedbugs/issue19040.go xfail entries for Darwin and Linux Go 1.24/1.25/1.26.
• Refreshes affected LITTEST IR goldens for generated wrapper nil checks.

Local validation:

• go test ./cl ./ssa -count=1
• go test ./test/go -run TestValueMethodWrapperNilPointerPanic -count=1
• go run ./cmd/llgo run "$(go env GOROOT)/test/fixedbugs/issue19040.go"
• go test ./test/goroot -run TestGoRootRunCases -count=1 -timeout 30m -args -goroot "$(go env GOROOT)" -case "fixedbugs/issue19040.go" -xfail -progress 30s

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!