configure: add missing avx2 support check

AVX2 support was introduced in Yasm 1.2.0 and NASM 2.10, and the
oldest versions currently supported are Yasm 0.8.0 and NASM 2.03
Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

configure

@@ -4313,6 +4313,7 @@ EOF
 
         check_yasm "movbe ecx, [5]" && enable yasm ||
             die "yasm/nasm not found or too old. Use --disable-yasm for a crippled build."
+        check_yasm "vextracti128 xmm0, ymm0, 0"      || disable avx2_external
         check_yasm "vpmacsdd xmm0, xmm1, xmm2, xmm3" || disable xop_external
         check_yasm "vfmadd132ps ymm0, ymm1, ymm2"    || disable fma3_external
         check_yasm "vfmaddps ymm0, ymm1, ymm2, ymm3" || disable fma4_external