Remove Og from debug mode

Last time I used gdb, iterating over a directory's `Indexes`, each uint256 printed as `<optimized out>`.

Debug mode is for debugging ...

SConstruct

@@ -369,11 +369,9 @@ def config_env(toolchain, variant, env):
                 env.Append(CPPDEFINES={
                     '_FORTIFY_SOURCE': 2
                     })
-                # Build debuggable but still optimized executable
-                # via -Og switch introduced in GCC 4.8
                 env.Append(CCFLAGS=[
-                    '-Og'           # Debuggable optimizations, new in GCC 4.8
-                ])
+                    '-O0'
+                    ])
 
     elif toolchain == 'msvc':
         env.Append (CPPPATH=[