This patch mainly made the following changes:
- Support AVX-VNNI instructions;
- Support more complex FeatureList. By default, ',' is prior than '|'. And parentheses is supported;
- Introduce ExplicitVEXPrefix flag so that vpdpbusd/vpdpbusds/vpdpbusds/vpdpbusds instructions only use vex-encoding when user explicity add {vex} prefix.
Pull this out? This and the CodeGenFunction.* changes seem to be worth a separate patch