Split gen_expr_binop_rest

Split gen_expr_binop_rest

This splits gen_expr_binop_rest into two overloads.  One overload
retains the "pc" parameter, while the other does not, and furthermore
does not call gen_expr on the left-hand-side.  This split is useful
for subsequent patches in the new expression evaluation approach.

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

	* ax-gdb.c (gen_expr_binop_rest): Remove "pc" parameter.
	(gen_expr_binop_rest): New overload.