waf: rename --enable-sdl to --enable-sdl1

Grossly misleading.

wscript

@@ -406,7 +406,7 @@ audio_output_features = [
         'func': check_pkg_config('sdl2'),
         'default': 'disable'
     }, {
-        'name': '--sdl',
+        'name': '--sdl1',
         'desc': 'SDL (1.x)',
         'deps_neg': [ 'sdl2' ],
         'func': check_pkg_config('sdl'),

wscript_build.py

@@ -141,7 +141,7 @@ def build(ctx):
         ( "audio/out/ao_portaudio.c",            "portaudio" ),
         ( "audio/out/ao_pulse.c",                "pulse" ),
         ( "audio/out/ao_rsound.c",               "rsound" ),
-        ( "audio/out/ao_sdl.c",                  "sdl" ),
+        ( "audio/out/ao_sdl.c",                  "sdl1" ),
         ( "audio/out/ao_sdl.c",                  "sdl2" ),
         ( "audio/out/ao_sndio.c",                "sndio" ),
         ( "audio/out/ao_wasapi.c",               "wasapi" ),