Use +dynamic-system-linker for aarch64 -> aarch64 musl

Author: hamishmack

compiler/ghc/default.nix

@@ -323,8 +323,8 @@ let
         " '*.*.ghc.*.opts += -fexternal-dynamic-refs'"
       # The fact that we need to set this here is pretty idiotic. GHC should figure this out on it's own.
       # Either have a runtime flag/setting to disable it or if dlopen fails, remember that it failed and
-      # fall back to non-dynamic. We only have x86_64 dynamic linker with musl.
-      + lib.optionalString (targetPlatform.isAndroid || (targetPlatform.isMusl && !targetPlatform.isx86))
+      # fall back to non-dynamic. We only have dynamic linker with musl if host and target arch match.
+      + lib.optionalString (targetPlatform.isAndroid || (targetPlatform.isMusl && haskell-nix.haskellLib.isCrossTarget))
         " '*.ghc.cabal.configure.opts += --flags=-dynamic-system-linker'"
       # The following is required if we build on aarch64-darwin for aarch64-iOS. Otherwise older
       # iPhones/iPads/... won't understand the compiled code, as the compiler will emit LDSETALH