compiler: alignof(func) is 1 pointer, not 2

This ensures that an embedded [0]func() never ends up being larger
than 1 pointer, which is requried by protobuf processing code.

testdata/reflect.txt

@@ -405,6 +405,9 @@ offset for int64 matches: true
 offset for complex128 matches: true
 type assertion succeeded for unreferenced type
 
+alignment / offset:
+struct{[0]func(); byte}: true
+
 struct tags
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