Add corresponding clc functions, which are implemented with clang
__scoped_atomic builtins. OpenCL functions are implemented as a wrapper
over clc functions.
Also change legacy atomic_inc and atomic_dec to re-use the newly added
clc_atomic_inc/dec implementations. llvm-diff only no change to
atomic_inc and atomic_dec in bitcode.
Notes:
* Generic OpenCL built-ins functions uses __ATOMIC_SEQ_CST and
__MEMORY_SCOPE_DEVICE for memory order and memory scope parameters.
* OpenCL atomic_*_explicit, atomic_flag* built-ins are not implemented
yet.
* OpenCL built-ins of atomic_intptr_t, atomic_uintptr_t, atomic_size_t
and atomic_ptrdiff_t types are not implemented yet.
* llvm-diff shows no change to nvptx64--nvidiacl.bc and
amdgcn--amdhsa.bc since __opencl_c_atomic_order_seq_cst and
__opencl_c_atomic_scope_device are not defined in these two targets.
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