Implement OpenCL binary operations

Implement OpenCL binary operations

This implements various OpenCL binary operations, adding a new
template class to do so.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* opencl-lang.c (opencl_relop, eval_opencl_assign): No longer
	static.  Change parameters.
	(eval_opencl_assign): No longer static.  Add "op" parameter.
	(evaluate_subexp_opencl): Update.
	* c-exp.h (opencl_binop_operation): New template class.
	(opencl_assign_operation, opencl_equal_operation)
	(opencl_notequal_operation, opencl_less_operation)
	(opencl_gtr_operation, opencl_geq_operation)
	(opencl_leq_operation): New typedefs.