**Issue #:**
internal V1647663988

[SEV-SNP enabled EC2 instances](https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/sev-snp.html) crash when using AWS CLI to upload with checksum algorithm CRC64NVME. [AWS CLI v2](https://github.com/aws/aws-cli/tree/v2) uses aws-c-common under the hood to do CRC64NVME.

**Investigation:**
aws-c-common has checks for AVX support, using [CPUID](https://en.wikipedia.org/wiki/CPUID). But apparently, just because CPUID reports that it can do AVX, doesn't necessarily mean it's enabled by the OS. On SEV-SNP enabled instances, AVX is not allowed.

GCC had the same bug until 7.4: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85100

Stackoverflow question: https://stackoverflow.com/questions/72522885/are-the-xgetbv-and-cpuid-checks-sufficient-to-guarantee-avx2-support

**Description of changes:**
* Do further checks before deciding that AVX can be used.
* Move all Intel feature detection into 1 function.
   * This is simpler, it's how we're doing feature detection on some other architectures.
   * Add checks to find the max value that CPUID accepts. We weren't doing this before.