configure: Adjust AVX assembler check.

Older nasm versions have trouble assembling certain AVX instructions, but the
current AVX check did not detect this. Update the check to use an instruction
that triggers the nasm problem.

configure

@@ -2729,7 +2729,7 @@ EOF
 
         check_yasm "pextrd [eax], xmm0, 1" && enable yasm ||
             die "yasm not found, use --disable-yasm for a crippled build"
-        check_yasm "vpaddw xmm0, xmm0, xmm0" || disable avx
+        check_yasm "vextractf128 xmm0, ymm0, 0" || disable avx
     fi
 
     case "$cpu" in