CPU feature checking - require SSE4.2

 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 SSE4.2 and refuses to install
 on unsupported hardware.
 .
 SSE4.2 added string and text processing instructions that perform character
 searches and comparison on two operands of 16 bytes at a time. It is
 available on Intel processors since Nehalem (circa 2008), but notably not
 on anything AMD until the Bulldozer (15h, in 2011) and Jaguar (16h, in
 2013) families.