cleanup meson.build

meson.build

@@ -8,10 +8,8 @@ project('emper-echo-server', 'c', 'cpp',
 		  'werror=true',
 		])
 
-add_project_arguments(
-	'-D_GNU_SOURCE',
-	language: 'c'
-)
+run_target('iwyu', command: 'tools/check-iwyu')
+
 conf_data = configuration_data()
 option_async_io = get_option('async_io')
 conf_data.set('USE_ASYNC_IO', option_async_io)
@@ -28,12 +26,7 @@ else
 endif
 
 emper_dep = emper_proj.get_variable('emper_dep')
-
 dependencies = [emper_dep]
 
-run_target('iwyu',
-           command: 'tools/check-iwyu')
-
-
 subdir('src')
 subdir('test')