modpost: Ignore unresolved section bounds symbols

modpost: Ignore unresolved section bounds symbols

In preparation for klp-build livepatch module creation tooling,
suppress warnings for unresolved references to linker-generated
__start_* and __stop_* section bounds symbols.

These symbols are expected to be undefined when modpost runs, as they're
created later by the linker.

Cc: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Petr Mladek <pmladek@suse.com>
Tested-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>