Move loop and switch tree data structures from cp/ to c-family/.

Move loop and switch tree data structures from cp/ to c-family/.

This patch moves the definitions for DO_STMT, FOR_STMT, WHILE_STMT,
SWITCH_STMT, BREAK_STMT, and CONTINUE_STMT from the C++ front end to
c-family.  This includes the genericizers, pretty-printers, and dump
support as well as the tree definitions and accessors.  Some related
code for OMP_FOR and similar OMP constructs is also moved.

2020-08-12  Sandra Loosemore  <sandra@codesourcery.com>

	gcc/c-family/
	* c-common.c (c_block_may_fallthrough): New, split from
	cxx_block_may_fallthrough in the cp front end.
	(c_common_init_ts): Move handling of loop and switch-related
	statements here from the cp front end.
	* c-common.def (FOR_STMT, WHILE_STMT, DO_STMT): Move here from
	cp front end.
	(BREAK_STMT, CONTINUE_STMT, SWITCH_STMT): Likewise.
	* c-common.h (c_block_may_fallthru): Declare.
	(bc_state_t): Move here from cp front end.
	(save_bc_state, restore_bc_state): Declare.
	(c_genericize_control_stmt): Declare.
	(WHILE_COND, WHILE_BODY): Likewise.
	(DO_COND, DO_BODY): Likewise.
	(FOR_INIT_STMT, FOR_COND, FOR_EXPR, FOR_BODY, FOR_SCOPE): Likewise.
	(SWITCH_STMT_COND, SWITCH_STMT_BODY): Likewise.
	(SWITCH_STMT_TYPE, SWITCH_STMT_SCOPE): Likewise.
	(SWITCH_STMT_ALL_CASES_P, SWITCH_STMT_NO_BREAK_P): Likewise.
	(LABEL_DECL_BREAK, LABEL_DECL_CONTINUE): Likewise.
	* c-dump.c (dump_stmt): Copy from cp front end.
	(c_dump_tree): Move code to handle structured loop and switch
	tree nodes here from cp front end.
	* c-gimplify.c: Adjust includes.
	(enum bc_t, bc_label, begin_bc_block, finish_bc_block): Move from
	cp front end.
	(save_bc_state, restore_bc_state): New functions using old code
	from cp front end.
	(get_bc_label, expr_loc_or_loc): Move from cp front end.
	(genericize_c_loop): Move from cp front end.
	(genericize_for_stmt, genericize_while_stmt): Likewise.
	(genericize_do_stmt, genericize_switch_stmt): Likewise.
	(genericize_continue_stmt, genericize_break_stmt): Likewise.
	(genericize_omp_for_stmt): Likewise.
	(c_genericize_control_stmt): New function using code split from
	cp front end.
	(c_genericize_control_r): New.
	(c_genericize): Call walk_tree with c_genericize_control_r.
	* c-pretty-print.c (c_pretty_printer::statement): Move code to handle
	structured loop and switch tree nodes here from cp front end.

	gcc/cp/
	* cp-gimplify.c (enum bc_t, bc_label): Move to c-family.
	(begin_bc_block, finish_bc_block, get_bc_label): Likewise.
	(genericize_cp_loop): Likewise.
	(genericize_for_stmt, genericize_while_stmt): Likewise.
	(genericize_do_stmt, genericize_switch_stmt): Likewise.
	(genericize_continue_stmt, genericize_break_stmt): Likewise.
	(genericize_omp_for_stmt): Likewise.
	(cp_genericize_r): Call c_genericize_control_stmt instead of
	above functions directly.
	(cp_genericize): Call save_bc_state and restore_bc_state instead
	of manipulating bc_label directly.
	* cp-objcp-common.c (cxx_block_may_fallthru): Defer to
	c_block_may_fallthru instead of handling SWITCH_STMT here.
	(cp_common_init_ts): Move handling of loop and switch-related
	statements to c-family.
	* cp-tree.def (FOR_STMT, WHILE_STMT, DO_STMT): Move to c-family.
	(BREAK_STMT, CONTINUE_STMT, SWITCH_STMT): Likewise.
	* cp-tree.h (LABEL_DECL_BREAK, LABEL_DECL_CONTINUE): Likewise.
	(WHILE_COND, WHILE_BODY): Likewise.
	(DO_COND, DO_BODY): Likewise.
	(FOR_INIT_STMT, FOR_COND, FOR_EXPR, FOR_BODY, FOR_SCOPE): Likewise.
	(SWITCH_STMT_COND, SWITCH_STMT_BODY): Likewise.
	(SWITCH_STMT_TYPE, SWITCH_STMT_SCOPE): Likewise.
	(SWITCH_STMT_ALL_CASES_P, SWITCH_STMT_NO_BREAK_P): Likewise.
	* cxx-pretty-print.c (cxx_pretty_printer::statement): Move code
	to handle structured loop and switch tree nodes to c-family.
	* dump.c (cp_dump_tree): Likewise.

	gcc/
	* doc/generic.texi (Basic Statements): Document SWITCH_EXPR here,
	not SWITCH_STMT.
	(Statements for C and C++): Rename node to reflect what
	the introduction already says about sharing between C and C++
	front ends.  Copy-edit and correct documentation for structured
	loops and switch.