objtool: Fix false-positive "ignoring unreachables" warning

There's no need to try to automatically disable unreachable warnings if
they've already been manually disabled due to CONFIG_KCOV quirks.

This avoids a spurious warning with a KCOV kernel:

  fs/smb/client/cifs_unicode.o: warning: objtool: cifsConvertToUTF16.part.0+0xce5: ignoring unreachables due to jump table quirk

Fixes: eeff7ac ("objtool: Warn when disabling unreachable warnings")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/5eb28eeb6a724b7d945a961cfdcf8d41e6edf3dc.1744238814.git.jpoimboe@kernel.org
Closes: https://lore.kernel.org/r/202504090910.QkvTAR36-lkp@intel.com/

Author: jpoimboe

tools/objtool/arch/x86/special.c

@@ -126,7 +126,7 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
 	 * indicates a rare GCC quirk/bug which can leave dead
 	 * code behind.
 	 */
-	if (reloc_type(text_reloc) == R_X86_64_PC32) {
+	if (!file->ignore_unreachables && reloc_type(text_reloc) == R_X86_64_PC32) {
 		WARN_INSN(insn, "ignoring unreachables due to jump table quirk");
 		file->ignore_unreachables = true;
 	}