symtab-reader: Remove an over-agressive assertion

symtab-reader: Remove an over-agressive assertion

In symtab::load, the symtab reader walks the symbol table and records
each relation "symbol <-> address".
So, the relation "foo <-> address-of-foo" is going to be recorded.
The relation "foo.cfi <-> address-of-foo.cfi" is going to be recorded
as well.

But then, because the symbol foo.cfi has a special meaning, in the
realm of "control flow integrity", the relation "foo.cfi <->
address-of-foo.cfi" (as well as all the *.cfi <-> address-of*.cfi
relations) is going to be recorded (again but) in a particular way by
calling symtab::add_alternative_address_lookups.

The problem is that in, symtab::add_alternative_address_lookups there
is an assert that (wrongly) assumes that the relation foo.cfi <->
address-of-foo.cfi is being seen for the first time.  This is wrong
because the loop in symtab::load that records all the "symbol <->
address" relations has seen and recorded this foo.cfi <->
address-of-foo.cfi relation once already.

This patch removes that assert so that the kernel referred to in the bug
report of PR26646, as mentioned in
https://sourceware.org/bugzilla/show_bug.cgi?id=26646#c5, can be
processed by abidw without crashing.

	* src/abg-symtab-reader.cc
	(symtab::add_alternative_address_lookups): Remove over-aggressive
	assert.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>
Reviewed-by: Giuliano Procida <gprocida@google.com>