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>

scripts/mod/modpost.c

@@ -606,6 +606,11 @@ static int ignore_undef_symbol(struct elf_info *info, const char *symname)
 		    strstarts(symname, "_savevr_") ||
 		    strcmp(symname, ".TOC.") == 0)
 			return 1;
+
+	/* ignore linker-created section bounds variables */
+	if (strstarts(symname, "__start_") || strstarts(symname, "__stop_"))
+		return 1;
+
 	/* Do not ignore this symbol */
 	return 0;
 }