Allow duplicate record fields in pattern synonyms

DuplicateRecordFields seems to not work for pattern synonyms

{-# Language PatternSynonyms, DuplicateRecordFields, NamedFieldPuns #-}

pattern A{x} = Just x
pattern B{x} = Just x

tg4t.hs:4:11: error: …
    Multiple declarations of ‘x’
    Declared at: /tmp/tg4t.hs:3:11
                 /tmp/tg4t.hs:4:11
Compilation failed.

Trac metadata

Trac field	Value
Version
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
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CC	mpickering
Operating system
Architecture