[Driver] Provide CLI for configuring SPIR-V extensions

[AGindinson]

In specific cases, the compiler user may want to enable/disable certain or all SPIR-V extensions for the forwards SPIR-V translation. For example, whenever a third-party OpenCL Runtime is to be used under the hood of DPC++ RT, it can be necessary to pass --spirv-ext=-all to the translator.

Possible driver solutions:

1. A CLI option to disable all SPIR-V extensions (tailored to the exemplary use-case)
2. A CLI option to pass a custom list of SPIR-V extensions for the translator command (with the same +/-, comma-separated syntax or as a configuration file of a sort)
3. A CLI option to pass any set of additional options to the SPIR-V Translator

3 is the broadest option, and may also cover some of the future problems.

[mdtoguchi]

Fixed here: bcf6885
Introduces -Xspirv-translator <arg> to pass any arguments to the translation step.