[commit: ghc] wip/T8584's head updated: Add support for pattern synonym type signatures. Syntax is of the form (d4530b6)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

Branch 'wip/T8584' now includes:

     4ba884b Optimise `Identity` instances with `coerce`
     8e0a480 rts: remove old-style field designator extension (#9396)
     101c62e The test runner now also works under the msys-native Python.
     6fc78fd Refactor: use System.FilePath.splitSearchPath
     66c0513 Update documentation for "Batch compiler mode"
     00c1a30 Implement new Foldable methods for HsPatSynDetails
     5db61ea Turn CoreWriter into a newtype; fix comment
     5c09893 Add remaining <unknown>s and comments to .mailmap
     7ef0971 Filter input to abiHash early
     b3df5f6 template-haskell: Missing instances for Rational and ().
     b047733 add missing instances for Loc and a few missing Eq instances
     146dd13 Only test for bug #9439 when llvm is installed
     53a4742 Allow -dead_strip linking on platforms with .subsections_via_symbols
     33c029f make TcRnMonad.lhs respect -ddump-to-file
     4dd87c5 use correct word size for shiftRightLogical and removeOp32
     80f6fc1 compiler/main: fixes #9776
     d87fa34 arm64: 64bit iOS and SMP support (#7942)
     bc2289e ghc generates more user-friendly error messages
     c6e12e6 Make calling conventions in template haskell Syntax.hs consistent with those in ghc ForeignCall.hs this impliments #9703 from ghc trac
     8cbd25a Make Data.Functor.Identity trustworthy again
     3b81309 Update shift/reduce conflict number in parser
     d4530b6 Add support for pattern synonym type signatures. Syntax is of the form