objtool: Fix Clang jump table detection

With Clang, there can be a conditional forward jump between the load of
the jump table address and the indirect branch.

Fixes the following warning:

  vmlinux.o: warning: objtool: ___bpf_prog_run+0x1c5: sibling call from callable instruction with modified stack frame

Reported-by: Arnd Bergmann <arnd@arndb.de>
Closes: https://lore.kernel.org/a426d669-58bb-4be1-9eaa-6f3d83109e2d@app.fastmail.com
Link: https://patch.msgid.link/7d8600caed08901b6679767488acd639f6df9688.1773071992.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

Author: jpoimboe

tools/objtool/check.c

@@ -2184,12 +2184,11 @@ static void mark_func_jump_tables(struct objtool_file *file,
 			last = insn;
 
 		/*
-		 * Store back-pointers for unconditional forward jumps such
+		 * Store back-pointers for forward jumps such
 		 * that find_jump_table() can back-track using those and
 		 * avoid some potentially confusing code.
 		 */
-		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
-		    insn->offset > last->offset &&
+		if (insn->jump_dest &&
 		    insn->jump_dest->offset > insn->offset &&
 		    !insn->jump_dest->first_jump_src) {