JuliaGPU/GPUCompiler.jl: v0.15.0

Diff since v0.14.1

Closed issues:

• Improper metadata cloning for kernels (#288)

Merged pull requests:

• Add a hook to post-process all IR. (#315) (@maleadt)
• Simplify IR cloning. (#316) (@maleadt)
• Don't drop constants while cloning IR. (#319) (@maleadt)
• Use function type in fspec instead of value (#320) (@wsmoses)
• Update manifest (#321) (@github-actions[bot])