Remove -O0 optimize flag from debuggable flags to enable debuggable optimized builds

This allows debug symbol information to be included for optimized builds. This
may not always be useful for debugging but it is necessary to use profiling
tools like perf.

The default optimize level is -O0 if no other optimize flag is specified so the
optimization level will be the same unless overridden.

wscript

@@ -35,7 +35,7 @@ Context.Context.is_tracks_build = is_tracks_build
 compiler_flags_dictionaries= {
     'gcc' : {
         # Flags required when building a debug build
-        'debuggable' : [ '-O0', '-g' ],
+        'debuggable' : [ '-g' ],
         # Flags required for the linker (if any) when building a debug build
         'linker-debuggable' : '',
         # Flags required when building a non-debug optimized build