[CSGen] Favor CGFloat operator overloads for floating-pointer literal arguments

If argument is a floating-point literal, with newly introduced implicit
Double<->CGFloat conversion, sometimes it's better to choose a concrete
function/operator overload on `CGFloat` even if it's not a default literal
type e.g. `let _: CGFloat = min(1.0, log(<CGFloat value>))` shouldn't form
solutions with `Double` arguments since it would result in multiple
implicit conversions, it's better to use a `CGFloat` type for the arguments.

Author: xedin

lib/Sema/CSGen.cpp

@@ -414,7 +414,8 @@ namespace {
         // If there is a default type for the literal protocol, check whether
         // it is the same as the parameter type.
         // Check whether there is a default type to compare against.
-        if (paramTy->isEqual(defaultType))
+        if (paramTy->isEqual(defaultType) ||
+            (defaultType->isDoubleType() && paramTy->isCGFloatType()))
           return true;
       }
     }