audio_filter: fix no-NEON ARM builds

modules/audio_filter/Makefile.am

@@ -56,8 +56,10 @@ libtrivial_channel_mixer_plugin_la_SOURCES = \
 	audio_filter/channel_mixer/trivial.c
 libsimple_channel_mixer_plugin_la_SOURCES = \
 	audio_filter/channel_mixer/simple.c
+libsimple_channel_mixer_plugin_la_CFLAGS =
 if HAVE_NEON
 libsimple_channel_mixer_plugin_la_SOURCES += arm_neon/simple_channel_mixer.S
+libsimple_channel_mixer_plugin_la_CFLAGS += -DCAN_COMPILE_ARM
 endif
 
 audio_filter_LTLIBRARIES += \

modules/audio_filter/channel_mixer/simple.c

@@ -258,7 +258,7 @@ static void DoWork_6_1_to_5_x( filter_t * p_filter,  block_t * p_in_buf, block_t
     }
 }
 
-#if defined (__arm__)
+#if defined (CAN_COMPILE_ARM)
 #include "simple_neon.h"
 #define GET_WORK(in, out) GET_WORK_##in##_to_##out##_neon()
 #else