CPU feature checking - require x86-64-v2

 The packages in the isa-support family probe for microprocessor Instruction
 Set Architecture features such as SSE3. By refusing to install on machines
 lacking a required feature, they allow ISA requirements to be handled in
 terms of package dependencies.
 .
 This is a mostly dummy package which checks for x86-64-v2 and
 refuses to install on unsupported hardware.
 .
 This is the Micro-Architecture Levels version 2 as defined by the
 amd64 ABI document.
 This includes:
 - cmov instruction (CMOV instruction set),
 - cmpxchg8b ant other 64 bits atomics instruction (CX8 instruction set),
 - MMX a single instruction, multiple data (SIMD) instruction set,
 - streaming SIMD Extensions (SSE) set, a single instruction, multiple data
   (SIMD) instruction set extension,
 - SSE2 an incremental upgrade to SSE.
 - cmpxchg16b ant other 128 bits atomics instruction (CX16 instruction set),
 - SSE3, also called PNI (Prescott New Instructions), is an incremental upgrade
   to SSE2
 - SSE4.1 added a dot product instruction and additional integer instructions.
 - SSE4.2 added string and text processing instructions that perform character
   searches and comparison on two operands of 16 bytes at a time.
 - SSSE3 or Supplemental Streaming SIMD Extension 3.
 .
 The corresponding micro-architecture level from the x86-64 psABI.
 On ABIs other than the x86-64 psABI they select the same CPU features
 as the x86-64 psABI documents for the particular micro-architecture level.