[opus] [RFC PATCH v1] arm: kf_bfly4: Introduce ARM neon intrinsics

[Timothy B. Terriberry]

Viswanath Puttagunta wrote:
> a. Will the approach of enabling this optimization using
> --enable-armv7-neon-float or similar flag be acceptable to begin with?
>
> or
>
> b. Should the "AS_IF([test x"${enable_asm}" = x"yes"]".. section in
> configure.ac be re-written?

Automatic detection of compiler support in configure (in addition to 
run-time checks) would be preferable.

We used a manual switches for, e.g., the SSE 4.2 intrinsics, just 
because the submitted auto-detection code was not very reliable, and no 
one has written anything better yet.