Misc build fixes (#21413)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/core/bug_on.h

   #define BUG_ON(V...) do { SERIAL_ECHOPAIR(ONLY_FILENAME, __LINE__, ": "); SERIAL_ECHOLNPAIR(V); SERIAL_FLUSHTX(); *(char*)0 = 42; } while(0)
 #elif ENABLED(MARLIN_DEV_MODE)
   // Don't stop the CPU here, but at least dump the bug on the serial port
-  #define BUG_ON(V...) do { SERIAL_ECHOPAIR(ONLY_FILENAME, __LINE__, ": BUG!\n"); SERIAL_ECHOLNPAIR(V); SERIAL_FLUSHTX(); } while(0)
+  //#define BUG_ON(V...) do { SERIAL_ECHOPAIR(ONLY_FILENAME, __LINE__, ": BUG!\n"); SERIAL_ECHOLNPAIR(V); SERIAL_FLUSHTX(); } while(0)
+  #define BUG_ON(V...) NOOP
 #else
   // Release mode, let's ignore the bug
   #define BUG_ON(V...) NOOP

Marlin/src/gcode/bedlevel/mbl/G29.cpp

       // For each G29 S2...
       if (mbl_probe_index == 0) {
         // Move close to the bed before the first point
-        do_blocking_move_to_z(0);
+        do_blocking_move_to_z(MANUAL_PROBE_START_Z);
       }
       else {
         // Save Z for the previous mesh position

Marlin/src/pins/ramps/pins_RAMPS.h

  *         7 | 11
  */
 
+#if ENABLED(AZSMZ_12864) && DISABLED(ALLOW_SAM3X8E)
+  #error "No pins defined for RAMPS with AZSMZ_12864."
+#endif
+
 #include "env_validate.h"
 
 // Custom flags and defines for the build
     #elif ENABLED(AZSMZ_12864)
 
       // Pins only defined for RAMPS_SMART currently
-      #if DISABLED(IS_RAMPS_SMART)
-        #error "No pins defined for RAMPS with AZSMZ_12864."
-      #endif
 
     #elif IS_TFTGLCD_PANEL