artiq-board: fix check for constraint errors

artiq/artiq-board.nix

@@ -52,10 +52,14 @@ in pkgs.python3Packages.buildPythonPackage rec {
     ''
     ${buildenv}/bin/artiq-dev -c "export CARGO_HOME=${cargoVendored}; ${buildCommand}"
     '';
-  preCheck = ''
+  checkPhase = ''
     # Search for PCREs in the Vivado output to check for errors
-    function check_log() {
-      if [ $(grep -Pe "$1" artiq_${target}/${variant}/gateware/vivado.log) != 1 ]; then
+    check_log() {
+      set +e
+      grep -Pe "$1" artiq_${target}/${variant}/gateware/vivado.log
+      FOUND=$?
+      set -e
+      if [ $FOUND != 1 ]; then
         exit 1
       fi
     }