[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/ios.py

@@ -79,8 +79,3 @@ def generate(env):
 
     env.Append(CCFLAGS=["-isysroot", env["IOS_SDK_PATH"]])
     env.Append(LINKFLAGS=["-isysroot", env["IOS_SDK_PATH"], "-F" + env["IOS_SDK_PATH"]])
-
-    if env["target"] == "debug":
-        env.Append(CCFLAGS=["-Og", "-g"])
-    elif env["target"] == "release":
-        env.Append(CCFLAGS=["-O3"])