arrow-cpp: Fix building x86_64-darwin on aarch_64-darwin (#193207)

When building x86_64-darwin emulated via Rosetta on aarch64-darwin, all
tests would fail with

> Illegal instruction: 4

this resolves that by never using Jemalloc on Darwin, since even though
`isAarch64` is false, it might “really” be aarch64-darwin.

pkgs/development/libraries/arrow-cpp/default.nix

@@ -39,7 +39,7 @@
 , zstd
 , enableShared ? !stdenv.hostPlatform.isStatic
 , enableFlight ? true
-, enableJemalloc ? !(stdenv.isAarch64 && stdenv.isDarwin)
+, enableJemalloc ? !stdenv.isDarwin
   # boost/process is broken in 1.69 on darwin, but fixed in 1.70 and
   # non-existent in older versions
   # see https://github.com/boostorg/process/issues/55