fex: fix and enable tests

This will still fail on Apple Silicon devices using 16K page size
kernels, but such systems are not supported by upstream, so there is
nothing we can do about that.

pkgs/by-name/fe/fex/package.nix

@@ -10,6 +10,7 @@
   nix-update-script,
   xxHash,
   fmt,
+  nasm,
 }:
 
 llvmPackages.stdenv.mkDerivation (finalAttrs: {
@@ -63,6 +64,8 @@ llvmPackages.stdenv.mkDerivation (finalAttrs: {
     ))
   ];
 
+  nativeCheckInputs = [ nasm ];
+
   buildInputs =
     [
       xxHash
@@ -85,7 +88,18 @@ llvmPackages.stdenv.mkDerivation (finalAttrs: {
   ];
 
   strictDeps = true;
-  doCheck = false; # broken on Apple silicon computers
+
+  # Unsupported on non-4K page size kernels (e.g. Apple Silicon)
+  doCheck = true;
+
+  # List not exhaustive, e.g. because they depend on an x86 compiler or some
+  # other difficult-to-build test binaries.
+  checkTarget = lib.concatStringsSep " " [
+    "asm_tests"
+    "api_tests"
+    "fexcore_apitests"
+    "emitter_tests"
+  ];
 
   # Avoid wrapping anything other than FEXConfig, since the wrapped executables
   # don't seem to work when registered as binfmts.