Implement binary comparison operations

Implement binary comparison operations

This implements the binary comparison operations via a template class.

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

	* expop.h (class comparison_operation): New.
	(equal_operation, notequal_operation, less_operation)
	(gtr_operation, geq_operation, leq_operation): New typedefs.
	* eval.c (eval_op_equal, eval_op_notequal, eval_op_less)
	(eval_op_gtr, eval_op_geq, eval_op_leq): No longer static.