add async_lib_try_syscall support

meson.build

@@ -12,8 +12,21 @@ add_project_arguments(
 	'-D_GNU_SOURCE',
 	language: 'c'
 )
+conf_data = configuration_data()
+option_async_io = get_option('async_io')
+conf_data.set('USE_ASYNC_IO', option_async_io)
+
+option_try_syscall = get_option('try_syscall')
+if option_try_syscall
+	if not option_async_io
+		error('try_syscall defined without async_io')
+	endif
+
+	emper_proj = subproject('emper', default_options: ['async_lib=true', 'async_lib_try_syscall=true'])
+else
+	emper_proj = subproject('emper', default_options: ['async_lib=true'])
+endif
 
-emper_proj = subproject('emper', default_options: ['async_lib=true'])
 emper_dep = emper_proj.get_variable('emper_dep')
 
 dependencies = [emper_dep]
@@ -21,8 +34,6 @@ dependencies = [emper_dep]
 run_target('iwyu',
            command: 'tools/check-iwyu')
 
-conf_data = configuration_data()
-conf_data.set('USE_ASYNC_IO', get_option('use_async_io'))
 
 subdir('src')
 subdir('test')

meson_options.txt

-option('use_async_io', type: 'boolean', value: true)
+option('async_io', type: 'boolean', value: true)
+option('try_syscall', type: 'boolean', value: true)