Handle block-local names for Ada

Handle block-local names for Ada

GNAT can generate a mangled name with "B_N" (where N is a number) in
the middle, like "hello__B_1__fourth.0".  This is used for names local
to a block.  Multiple levels of block-local name can also occur, a
possibility that was neglected by v1 of this patch.  This patch
changes gdb to handle these names.

The wild name matcher is updated a straightforward way.  The full
matcher is rewritten.  The hash function is updated to ensure that
this works.

This version does not seem to have the performance problems that
affected v1.  In particular, the previously-slow "bt" problem has been
fixed.

gdb/ChangeLog
2020-12-14  Tom Tromey  <tromey@adacore.com>

	* dictionary.c (language_defn::search_name_hash): Ignore "B".
	* ada-lang.c (advance_wild_match): Ignore "B".
	(full_match): Remove.
	(do_full_match): Rewrite.

gdb/testsuite/ChangeLog
2020-12-14  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/nested.exp: Add new tests.
	* gdb.ada/nested/hello.adb (Fourth, Fifth): New procedures.