[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/linux.py

@@ -18,11 +18,6 @@ def generate(env):
     env.Append(CCFLAGS=["-fPIC", "-Wwrite-strings"])
     env.Append(LINKFLAGS=["-Wl,-R,'$$ORIGIN'"])
 
-    if env["target"] == "debug":
-        env.Append(CCFLAGS=["-Og", "-g"])
-    elif env["target"] == "release":
-        env.Append(CCFLAGS=["-O3"])
-
     if env["arch"] == "x86_64":
         # -m64 and -m32 are x86-specific already, but it doesn't hurt to
         # be clear and also specify -march=x86-64. Similar with 32-bit.