Improve warning message if multi-release JARs are not supported

This is a follow up from my pervious PR [1]. Unfortunatly, it only
occured to me after it was merged that the warning message is
incomplete. In my case it was not the runtime environment which did
not support multi-release JARs, but the build system. This adjusts the
message accordingly.

1: apache#1760

Author: Flowdalic

log4j-api/src/main/java/org/apache/logging/log4j/util/StackLocator.java

@@ -80,7 +80,7 @@ public final class StackLocator {
         } catch (final Exception | LinkageError e) {
             if (Constants.JAVA_MAJOR_VERSION > 8) {
                 LowLevelLogUtil.log(
-                        "WARNING: Runtime environment does not support multi-release JARs. This will impact location-based features.");
+                        "WARNING: Runtime environment or build system does not support multi-release JARs. This will impact location-based features.");
             } else {
                 LowLevelLogUtil.log(
                         "WARNING: sun.reflect.Reflection.getCallerClass is not supported. This will impact location-based features.");