Starting with version 3.8, grep emits warning messages when pattern
contain spurious slashes:
grep '\+' /dev/null
grep: warning: stray \ before +
GHC’s testsuite does not expect that and fails.
* gnu/packages/patches/ghc-9.2-grep-warnings.patch: New file.
* gnu/local.mk: Add it.
* gnu/packages/haskell.scm (ghc-9.2)[native-inputs]: Add patch.
