Default to tar & zip over libarchive except on supported platforms

`libarchive` (the Haskell package, not its upstream C library) vendors
the `config.h` header files generated by autoconf for each platform it
supports instead of using autoconf (or even CMake, which the C library
offers as an option). So apart from those specific platforms, just use
`tar` & `zip`.

`lzma-static` currently does the same, but we're gonna fix it upstream
then update the minimum version bounds on our dependency of it.

cabal.project.release

@@ -2,9 +2,10 @@ import: cabal.project.common
 
 optimization: 2
 
--- The release project file always wants to build with -tar.
--- The tar flag is only there to circumvent complicated errors during
--- development, which sometimes happens due to libarchive.
+-- The release project file always wants to build with -tar on the
+-- platforms it supports (which are those it provides config.h files
+-- for). The tar flag is only there to circumvent complicated errors
+-- during development, which sometimes happens due to libarchive.
 package ghcup
     flags: +tui
 
@@ -32,3 +33,6 @@ elif os(freebsd)
                xz -system-xz
   package *
     ghc-options: -split-sections
+else
+  package ghcup
+    flags: +tar