frawk: disable llvm support (#381871)

pkgs/by-name/fr/frawk/package.nix

@@ -5,10 +5,16 @@
   libxml2,
   ncurses,
   zlib,
-  features ? [ "default" ],
-  llvmPackages_12,
+  features ? [
+    "use_jemalloc"
+    "allow_avx2"
+    "unstable"
+  ],
 }:
-
+# Don't allow LLVM support until https://github.com/ezrosent/frawk/issues/115 is resolved.
+assert lib.assertMsg (
+  !(lib.elem "default" features || lib.elem "llvm_backend" features)
+) "LLVM support has been dropped due to LLVM 12 EOL.";
 rustPlatform.buildRustPackage rec {
   pname = "frawk";
   version = "0.4.8";
@@ -30,13 +36,9 @@ rustPlatform.buildRustPackage rec {
   buildNoDefaultFeatures = true;
   buildFeatures = features;
 
-  preBuild =
-    lib.optionalString (lib.elem "default" features || lib.elem "llvm_backend" features) ''
-      export LLVM_SYS_120_PREFIX=${llvmPackages_12.llvm.dev}
-    ''
-    + lib.optionalString (lib.elem "default" features || lib.elem "unstable" features) ''
-      export RUSTC_BOOTSTRAP=1
-    '';
+  preBuild = lib.optionalString (lib.elem "default" features || lib.elem "unstable" features) ''
+    export RUSTC_BOOTSTRAP=1
+  '';
 
   # depends on cpu instructions that may not be available on builders
   doCheck = false;