Fix undeclared symbols in signal handler

Building with a custom toolchain (GCC 15, uClibc, kernel headers 5.10)
fails in netlink.c with errors like these:

pihole-ftl-6.5/src/signals.c:214:30: error: ‘BUS_MCEERR_AR’ undeclared (first use in this function)
  214 |                         case BUS_MCEERR_AR: log_info("     with code:  BUS_MCEERR_AR (Hardware memory error: action required)"); break;
      |                              ^~~~~~~~~~~~~
pihole-ftl-6.5/src/signals.c:214:30: note: each undeclared identifier is reported only once for each function it appears in
pihole-ftl-6.5/src/signals.c:215:30: error: ‘BUS_MCEERR_AO’ undeclared (first use in this function)
  215 |                         case BUS_MCEERR_AO: log_info("     with code:  BUS_MCEERR_AO (Hardware memory error: action optional)"); break;
      |                              ^~~~~~~~~~~~~

Bracket undeclared symbols with precompiler directives.

Signed-off-by: Andreas Ziegler <[email protected]>

Author: aeolio

src/signals.c

@@ -211,8 +211,14 @@ static void __attribute__((noreturn)) signal_handler(int sig, siginfo_t *si, voi
 			case BUS_ADRALN:    log_info("     with code:  BUS_ADRALN (Invalid address alignment)"); break;
 			case BUS_ADRERR:    log_info("     with code:  BUS_ADRERR (Non-existent physical address)"); break;
 			case BUS_OBJERR:    log_info("     with code:  BUS_OBJERR (Object specific hardware error)"); break;
+#if defined (BUS_MCEERR_AR)
+			// 2025-May: not defined by uClibc
 			case BUS_MCEERR_AR: log_info("     with code:  BUS_MCEERR_AR (Hardware memory error: action required)"); break;
+#endif
+#if defined (BUS_MCEERR_AO)
+			// 2025-May: not defined by uClibc
 			case BUS_MCEERR_AO: log_info("     with code:  BUS_MCEERR_AO (Hardware memory error: action optional)"); break;
+#endif
 			default:            log_info("     with code:  Unknown (%i)", si->si_code); break;
 		}
 	}