arm_neon: Force libtool to be in CC mode when using a custom as for iOS.

modules/arm_neon/Modules.am

+# When using a specific AS tool instead of gcc libtool goes mad
+# without this. (This is the case with iOS).
+LIBTOOL=@LIBTOOL@ --tag=CC
+
 AM_CFLAGS += $(ARM_NEON_CFLAGS)
 
 libaudio_format_neon_plugin_la_SOURCES = \