Restore some of --strict to BuildPackages script

#4384

The addition of the --parallel option to the bin/BuildPackages.sh
script unfortunately broke the operation of the --strict option.

This restores the functionality of --strict when --parallel is not used.

I am not 1337 enough to work out how to do catch the error codes
of parallel background processes!

bin/BuildPackages.sh

@@ -269,7 +269,7 @@ build_one_package() {
 date >> "$LOGDIR/fail.log"
 for PKG in "${PACKAGES[@]}"
 do 
-  ( 
+  (  # start a background process
   # cut off the ending slash (if exists)
   PKG="${PKG%/}"
   # cut off everything before the first slash to only keep the package name
@@ -307,6 +307,7 @@ do
     warning "$PKG does not seem to be a package directory, skipping"
   fi
   ) &
+  BUILD_PID=$!
   if [ "x$PARALLEL" = "xyes" ]; then
     # If more than 4 background jobs are running, wait for one to finish (if
     # <wait -n> is available) or for all to finish (if only <wait> is available)
@@ -315,7 +316,10 @@ do
     fi
   else
     # wait for this package to finish building
-    wait
+    if ! wait $BUILD_PID && [[ $STRICT = yes ]]
+    then
+      exit 1
+    fi
   fi;
 done
 # Wait until all packages are built, if in parallel