compiler: allow deferred panic

This is rare, but apparently some programs do this:

    defer panic("...")

This is emitted in the IR as a builtin function.

testdata/recover.txt

@@ -23,3 +23,7 @@ recovered: panic
 panic 1
 panic 2
 recovered: panic 2
+
+# defer panic
+defer panic
+recovered from deferred call: deferred panic