[SCons] Add "optimize" and "debug_symbols" options

optimize = auto|none|debug|speed|size|0|1|2|3
debug_symbol = True|False

optimize == "auto" will produce:
- "debug" for "debug" builds
- "speed" for "release" builds

tools/macos.py

@@ -48,8 +48,3 @@ def generate(env):
             "-Wl,-undefined,dynamic_lookup",
         ]
     )
-
-    if env["target"] == "debug":
-        env.Append(CCFLAGS=["-Og", "-g"])
-    elif env["target"] == "release":
-        env.Append(CCFLAGS=["-O3"])