objtool: Fix retpoline support for pre-ORC objtool

Objtool 1.0 (pre-ORC) produces the following warning when it encounters
a retpoline:

  arch/x86/crypto/camellia-aesni-avx2-asm_64.o: warning: objtool: .altinstr_replacement+0xf: return instruction outside of a callable function

That warning is meant to catch GCC bugs and missing ENTRY/ENDPROC
annotations, neither of which are applicable to alternatives.  Silence
the warning for alternative instructions, just like objtool 2.0 already
does.
Reported-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/objtool/builtin-check.c

@@ -1230,6 +1230,14 @@ static int validate_uncallable_instructions(struct objtool_file *file)
 
 	for_each_insn(file, insn) {
 		if (!insn->visited && insn->type == INSN_RETURN) {
+
+			/*
+			 * Don't warn about call instructions in unvisited
+			 * retpoline alternatives.
+			 */
+			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
+				continue;
+
 			WARN_FUNC("return instruction outside of a callable function",
 				  insn->sec, insn->offset);
 			warnings++;