WML unit tests: port ability to override strict mode from 1.14

The ability isn't needed in master because none of the unit tests call
deprecated functions here, but it may be useful in the future or make
cherry-picking of future changes easier.

(cherry-picked from commit 74d8cfa98e)

run_wml_tests

@@ -130,6 +130,7 @@ run_test()
 {
   # Argument 1 is the expected error code
   # Argument 2 is the name of the test scenario
+  # Argument 3 (optional) overrides strict mode (0 to disable, 1 to enable)
 
   preopts=""
   binary="$BinPath"
@@ -166,8 +167,13 @@ run_test()
     return 100
   fi
 
+  strict_mode=$3
+  if [ -z "$strict_mode" ]; then
+    strict_mode=$StrictMode
+  fi
+
   # If running strict, then set strict level to "warning"
-  if [ "$StrictMode" -eq 1 ]; then
+  if [ "$strict_mode" -eq 1 ]; then
     opts+="--log-strict=warning "
   fi