Parameterize cp_scan_for_anonymous_namespaces

Parameterize cp_scan_for_anonymous_namespaces

This changes cp_scan_for_anonymous_namespaces to use the
buildsym_compunit API, rather than the function-based API.

gdb/ChangeLog
2018-07-20  Tom Tromey  <tom@tromey.com>

	* stabsread.c (define_symbol): Update.
	* buildsym-legacy.h (get_buildsym_compunit): Declare.
	* dwarf2read.c (new_symbol): Update.
	* cp-support.h (cp_scan_for_anonymous_namespaces): Update.
	* cp-namespace.c: Include buildsym.h.
	(cp_scan_for_anonymous_namespaces): Add "compunit" parameter.
	* buildsym-legacy.c (get_buildsym_compunit): New function.