Build Oniro -base images using LLVM in addition to GCC

Description

Setup a parallel set of build jobs to kick-off LLVM builds for all our -base images.

We'd like both gcc and LLVM based builds to happen for Oniro. We can decide whether to default to LLVM for the official release later (after CI success and V&V does some testing on it)

Edited Jun 13, 2022 by Amit Kucheria

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