ghdl: fix llvm backend, add passthru.tests

pkgs/development/compilers/ghdl/test-simple.nix

@@ -0,0 +1,23 @@
+{ stdenv, ghdl-llvm, ghdl-mcode, backend }:
+
+let
+  ghdl = if backend == "llvm" then ghdl-llvm else ghdl-mcode;
+in
+stdenv.mkDerivation {
+  name = "ghdl-test-simple";
+  meta.timeout = 300;
+  nativeBuildInputs = [ ghdl ];
+  buildCommand = ''
+    cp ${./simple.vhd} simple.vhd
+    cp ${./simple-tb.vhd} simple-tb.vhd
+    mkdir -p ghdlwork
+    ghdl -a --workdir=ghdlwork --ieee=synopsys simple.vhd simple-tb.vhd
+    ghdl -e --workdir=ghdlwork --ieee=synopsys -o sim-simple tb
+  '' + (if backend == "llvm" then ''
+    ./sim-simple --assert-level=warning > output.txt
+  '' else ''
+    ghdl -r --workdir=ghdlwork --ieee=synopsys tb > output.txt
+  '') + ''
+    diff output.txt ${./expected-output.txt} && touch $out
+  '';
+}