Add separate labels for the start of public functions

This avoids having to use the public symbol name when jumping here,
on platforms where the public symbols have an underscore prefix.

Signed-off-by: Timothy B. Terriberry <tterribe@xiph.org>
Make the arm2gnu.pl converter handle apple specific details

This allows building the arm assembly for iOS.

This checks for the __APPLE__ preprocessor built-in define to
determine whether this extra handling should be enabled.

Signed-off-by: Timothy B. Terriberry <tterribe@xiph.org>
Fix iOS builds with assembly.

The patch in 76e831d917ff got us most of the way there, but
 out-of-tree builds required a second Makefile.am rule, which was
 missing @ARM2GNU_PARAMS@.
Also, the arm2gnu.pl was terminating argument processing on any
 argument beginning with --, rather than an argument that was just
 -- by itself (as is the normal convention in GNU programs).
That meant it never saw the --apple flag even when it was passed.

Thanks to Jonathan Lennox for the report and for testing.