ruby: add RUBY sticky option that must be set to add ruby to the build

Default is false

tests/SConscript

@@ -265,8 +265,9 @@ else:
     configs += ['simple-atomic', 'simple-timing', 'o3-timing', 'memtest',
                 'simple-atomic-mp', 'simple-timing-mp', 'o3-timing-mp']
 
-# Hack for Ruby
-configs += [c + '-ruby' for c in configs]
+if env['RUBY']:
+    # Hack for Ruby
+    configs += [c + '-ruby' for c in configs]
 
 cwd = os.getcwd()
 os.chdir(str(Dir('.').srcdir))