ghc-toolchain: Parse i686 triples

This is a moniker used for later 32-bit x86 implementations
(Pentium Pro and later).

Fixes #25691.

utils/ghc-toolchain/src/GHC/Toolchain/ParseTriple.hs

@@ -36,6 +36,7 @@ parseArch :: Cc -> String -> M Arch
 parseArch cc arch =
     case arch of
       "i386" -> pure ArchX86
+      "i686" -> pure ArchX86
       "x86_64" -> pure ArchX86_64
       "amd64" -> pure ArchX86_64
       "powerpc" -> pure ArchPPC