new compiler method get_argument_syntax

The compiler object now has get_argument_syntax method, which returns a string value of gcc, msvc, or an undefined value string value. This can be used to determine if a compiler uses gcc syntax (-Wfoo), msvc syntax (/w1234), or some other kind of arguments.

cc = meson.get_compiler('c')

if cc.get_argument_syntax() == 'msvc'
  if cc.has_argument('/w1235')
    add_project_arguments('/w1235', language : ['c'])
  endif
elif cc.get_argument_syntax() == 'gcc'
  if cc.has_argument('-Wfoo')
    add_project_arguments('-Wfoo', language : ['c'])
  endif
elif cc.get_id() == 'some other compiler'
  add_project_arguments('--error-on-foo', language : ['c'])
endif