Take anonymous scopes into account when comparing decls

Take anonymous scopes into account when comparing decls

This is another attempt at handling anonymous decls comparison.  It's
not the full blown method that I'd like, but this one seems to be fast
enough.  In this method, we take the immediate scope (and whether it's
anonymous or not) of the anonymous decl into account.

	* include/abg-interned-str.h (interned_string::clear): Add new
	member function.
	* src/abg-ir.cc (equals): In the overload for decl_base, consider
	the scope of the current (anonymous) decl.  If that scope is
	anonymous then take that into account as well.
	* tests/data/test-diff-pkg/spice-server-0.12.4-19.el7.x86_64-0.12.8-1.el7.x86_64-report-3.txt:
	Adjust.
	* tests/data/test-read-dwarf/PR22122-libftdc.so.abi: Likewise.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>