x86/bugs: Rename CONFIG_RETPOLINE => CONFIG_MITIGATION_RETPOLINE

Step 5/10 of the namespace unification of CPU mitigations related Kconfig options.

[ mingo: Converted a few more uses in comments/messages as well. ]

Suggested-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ariel Miculas <amiculas@cisco.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20231121160740.1249350-6-leitao@debian.org

tools/objtool/arch/x86/special.c

@@ -83,7 +83,7 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
  *    ensure the same register is used in the mov and jump instructions.
  *
- *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
+ *    NOTE: MITIGATION_RETPOLINE made it harder still to decode dynamic jumps.
  */
 struct reloc *arch_find_switch_table(struct objtool_file *file,
 				    struct instruction *insn)

tools/objtool/check.c

@@ -3984,7 +3984,7 @@ static int validate_retpoline(struct objtool_file *file)
 			} else
 				continue;
 		} else {
-			WARN_INSN(insn, "indirect %s found in RETPOLINE build",
+			WARN_INSN(insn, "indirect %s found in MITIGATION_RETPOLINE build",
 				  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
 		}