java: javac 9+ print their version to stdout not stderr

Fixes: #2569

mesonbuild/environment.py

@@ -803,8 +803,8 @@ class Environment:
             p, out, err = Popen_safe(exelist + ['-version'])
         except OSError:
             raise EnvironmentException('Could not execute Java compiler "%s"' % ' '.join(exelist))
-        version = search_version(err)
         if 'javac' in out or 'javac' in err:
+            version = search_version(err if 'javac' in err else out)
             return JavaCompiler(exelist, version)
         raise EnvironmentException('Unknown compiler "' + ' '.join(exelist) + '"')