crypto: aegis128/simd - build 32-bit ARM for v8 architecture explicitly

Now that the Clang compiler has taken it upon itself to police the
compiler command line, and reject combinations for arguments it views
as incompatible, the AEGIS128 no longer builds correctly, and errors
out like this:

  clang-10: warning: ignoring extension 'crypto' because the 'armv7-a'
  architecture does not support it [-Winvalid-command-line-argument]

So let's switch to armv8-a instead, which matches the crypto-neon-fp-armv8
FPU profile we specify. Since neither were actually supported by GCC
versions before 4.8, let's tighten the Kconfig dependencies as well so
we won't run into errors when building with an ancient compiler.
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: NNathan Chancellor <natechancellor@gmail.com>
Tested-by: NNathan Chancellor <natechancellor@gmail.com>
Reviewed-by: NNick Desaulniers <ndesaulniers@google.com>
Tested-by: NNick Desaulniers <ndesaulniers@google.com>
Reported-by: <ci_notify@linaro.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -309,6 +309,7 @@ config CRYPTO_AEGIS128
 config CRYPTO_AEGIS128_SIMD
 	bool "Support SIMD acceleration for AEGIS-128"
 	depends on CRYPTO_AEGIS128 && ((ARM || ARM64) && KERNEL_MODE_NEON)
+	depends on !ARM || CC_IS_CLANG || GCC_VERSION >= 40800
 	default y
 
 config CRYPTO_AEGIS128_AESNI_SSE2