build with -O2

Rsconscript

@@ -120,7 +120,7 @@ EOF
     env.add_builder(EfiImage)
     env.add_builder(BiosImage)
     env.add_builder(FontGen)
-    env["CCFLAGS"] += %w[-ffreestanding -Wall]
+    env["CCFLAGS"] += %w[-ffreestanding -Wall -O2]
     env["LDFLAGS"] += %w[-ffreestanding -nostdlib -T src/link.ld]
     env["LIBS"] += %w[gcc]
     env["OBJDUMP"] = "i686-elf-objdump"