[Features] Allow ExtensionMacros to be enabled in noasserts builds.

(cherry picked from commit ff8e3df)

Author: hborla

include/swift/Basic/Features.def

@@ -122,7 +122,7 @@ EXPERIMENTAL_FEATURE(CodeItemMacros, false)
 EXPERIMENTAL_FEATURE(TupleConformances, false)
 EXPERIMENTAL_FEATURE(InitAccessors, false)
 
-EXPERIMENTAL_FEATURE(ExtensionMacros, false)
+EXPERIMENTAL_FEATURE(ExtensionMacros, true)
 SUPPRESSIBLE_LANGUAGE_FEATURE(ExtensionMacroAttr, 0, "@attached(extension)", true)
 
 // FIXME: MoveOnlyClasses is not intended to be in production,