Utilize Binaryen's -O4

When specifying -O3 or -Oz, asc now automatically increases the optimize level to 4, then including costly non-LLVM optimizations for blocky code, in turn achieving similar results as an LLVM-based generator.

tests/compiler.js

@@ -123,7 +123,7 @@ tests.forEach(filename => {
       filename,
       "--baseDir", basedir,
       "--validate",
-      "--optimize",
+      "-O3",
       "--measure",
       "--binaryFile" // -> stdout
     ];