[AMDGPU] New clang option for emitting a waitcnt instruction after each memory instruction (#79236)

This patch introduces a new command-line option for clang, namely,
amdgpu-precise-mem-op (or precise-memory in the backend). When this option is specified, a waitcnt
instruction is generated after each memory load/store instruction. The
counter values are always 0, but which counters are involved depends on
the memory instruction.

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Co-authored-by: Jun Wang <jun.wang7@amd.com>