Add targets to emit SPIR-V targeted to Mesa's OpenCL support, using
SPIR-V 1.1.
Substantially based on Dave Airlie's earlier work.
libclc: spirv: remove step/smoothstep apis not defined for SPIR-V
libclc: disable inlines for SPIR-V builds
Reviewed By: jvesely, tstellar, jenatali
Differential Revision: https://reviews.llvm.org/D77589