Add overloaded debug_bb and debug_bb_n with dump flags

Add overloaded debug_bb and debug_bb_n with dump flags

Add overloads that accept a flags argument so we can print
debug_bb_n (5, TDF_DETAILS) in gdb, also the debug_bb_slim
variant would then be just a forwarder.

gcc/ChangeLog:

2020-10-26  Xionghu Luo  <luoxhu@linux.ibm.com>

	* cfg.c (debug_bb): New overloaded function.
	(debug_bb_n): New overloaded function.
	* cfg.h (debug_bb): New declaration.
	(debug_bb_n): New declaration.
	* print-rtl.c (debug_bb_slim): Call debug_bb with flags.