arc: Add prologue analysis

arc: Add prologue analysis

Add a prologue analysis that recognizes all instructions that may happen in
compiler-generated prologue, including various stores, core register moves,
subtraction and ENTER_S instruction that does a lot of prologue actions through
microcode.

Testcases cover various prologue scenarios, including instructions that are
spread across multiple 16-bit encodings (for example there are 7 encodings of
store instruction).

gdb/ChangeLog:

yyyy-mm-dd  Anton Kolesov  <anton.kolesov@synopsys.com>

	* arc-tdep.c (arc_frame_cache): Add support for prologue analysis.
	(arc_skip_prologue): Likewise.
	(arc_make_frame_cache): Likewise.
	(arc_pv_get_operand): New function.
	(arc_is_in_prologue): Likewise.
	(arc_analyze_prologue): Likewise.
	(arc_print_frame_cache): Likewise.
	(MAX_PROLOGUE_LENGTH): New constant.

gdb/doc/ChangeLog:

yyyy-mm-dd  Anton Kolesov  <anton.kolesov@synopsys.com>

	* gdb.texinfo (Synopsys ARC): Document "set debug arc 2".

gdb/testsuite/ChangeLog:

yyyy-mm-dd  Anton Kolesov  <anton.kolesov@synopsys.com>

	* gdb.arch/arc-analyze-prologue.S: New file.
	* gdb.arch/arc-analyze-prologue.exp: Likewise.