Well -W<option> turns the warning on , if you wanted specific warnings to be turned off, you would have to use -Wno-<option> or -Wno-error= . E.g.

build_flags = 
   -Wno-unused-variable
   -Wno-deprecated-declarations
   -Wno-comment
See GCC docs and stackoverflow.
 mchahn:
Also, how can I see the actual compiler commands?
Project tasks → Advanced → Verbose Build.