compiler: refactor when the optsize attribute is set

This commit has a few related changes:

  * It sets the optsize attribute immediately in the compiler instead of
    adding it to each function afterwards in a loop. This seems to me
    like the more appropriate way to do it.
  * It centralizes setting the optsize attribute in the transform
    package, to make later changes easier.
  * It sets the optsize in a few more places: to runtime.initAll and to
    WebAssembly i64 wrappers.

This commit does not affect the binary size of any of the smoke tests,
so should be risk-free.

transform/optimizer.go

@@ -68,12 +68,12 @@ func Optimize(mod llvm.Module, config *compileopts.Config, optLevel, sizeLevel i
 		OptimizeStringToBytes(mod)
 		OptimizeReflectImplements(mod)
 		OptimizeAllocs(mod, nil, nil)
-		err := LowerInterfaces(mod, sizeLevel)
+		err := LowerInterfaces(mod, config)
 		if err != nil {
 			return []error{err}
 		}
 
-		errs := LowerInterrupts(mod, sizeLevel)
+		errs := LowerInterrupts(mod, config)
 		if len(errs) > 0 {
 			return errs
 		}
@@ -97,7 +97,7 @@ func Optimize(mod llvm.Module, config *compileopts.Config, optLevel, sizeLevel i
 
 	} else {
 		// Must be run at any optimization level.
-		err := LowerInterfaces(mod, sizeLevel)
+		err := LowerInterfaces(mod, config)
 		if err != nil {
 			return []error{err}
 		}
@@ -105,7 +105,7 @@ func Optimize(mod llvm.Module, config *compileopts.Config, optLevel, sizeLevel i
 		if config.FuncImplementation() == "switch" {
 			LowerFuncValues(mod)
 		}
-		errs := LowerInterrupts(mod, sizeLevel)
+		errs := LowerInterrupts(mod, config)
 		if len(errs) > 0 {
 			return errs
 		}