Disable warning around -source 7 -release 7 for java version checker

The java version checker triggers some default warnings because it
targets java7:

```
> Task :distribution:tools:java-version-checker:compileJava FAILED
warning: [options] source value 7 is obsolete and will be removed in a future release
warning: [options] target value 7 is obsolete and will be removed in a future release
warning: [options] To suppress warnings about obsolete options, use -Xlint:-options.
error: warnings found and -Werror specified
```

Suppress this warning explicitly for this module.

Signed-off-by: Robert Muir <rmuir@apache.org>

distribution/tools/java-version-checker/build.gradle

@@ -12,6 +12,8 @@
 apply plugin: 'opensearch.build'
 
 targetCompatibility = JavaVersion.VERSION_1_7
+// targetting very old java versions enables a warning by default on newer JDK: disable it.
+compileJava.options.compilerArgs += '-Xlint:-options'
 
 // java_version_checker do not depend on core so only JDK signatures should be checked
 tasks.named('forbiddenApisMain').configure {