[aarch64] Vector Function ABI specifications for AArch64 - OpenMP 5.0 update

Hi all,

Arm just released a version of the Vector Function ABI specifications for AArch64 that uses the `declare variant` directive from OpenMP 5.0 to support user defined vector functions. The mechanism is introduced in chapter 4, and it is in beta release status to allow feedback from the open source community. Feedback needs to be provided at arm.eabi (at) arm.com by end of June 16th (AOE).

The document (version 2019Q1.1) can be retrieved at https://developer.arm.com/tools-and-software/server-and-hpc/arm-architecture-tools/arm-compiler-for-hpc/vector-function-abi

Kind regards,

Francesco