make FixedArrays feature available in non-assert compiler builds

Author: eeckstein

include/swift/Basic/Features.def

@@ -276,7 +276,7 @@ EXPERIMENTAL_FEATURE(ExtractConstantsFromMembers, false)
 EXPERIMENTAL_FEATURE(BitwiseCopyable, true)
 
 /// Enables the FixedArray data type.
-EXPERIMENTAL_FEATURE(FixedArrays, false)
+EXPERIMENTAL_FEATURE(FixedArrays, true)
 
 #undef EXPERIMENTAL_FEATURE_EXCLUDED_FROM_MODULE_INTERFACE
 #undef EXPERIMENTAL_FEATURE