[07/11] crypto: x86/curve25519 - support assemblers with no adx support

[07/11] crypto: x86/curve25519 - support assemblers with no adx support

Origin: https://git.zx2c4.com/wireguard-linux/commit?id=eaa48741603adc09009b96451293034e396b5ca3
Bug-Debian: https://bugs.debian.org/953569

Some older version of GAS do not support the ADX instructions, similarly
to how they also don't support AVX and such. This commit adds the same
build-time detection mechanisms we use for AVX and others for ADX, and
then makes sure that the curve25519 library dispatcher calls the right
functions.

Reported-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[bwh: commit 1579f1bc3b753d17a44de3457d5c6f4a5b14c752 upstream]

Gbp-Pq: Topic features/all/wireguard
Gbp-Pq: Name 0007-crypto-x86-curve25519-support-assemblers-with-no-adx.patch