Trust the bootloader to clear globals

Marlin/src/Marlin.cpp

             new_fanSpeeds[FAN_COUNT];
   #endif
   #if ENABLED(PROBING_FANS_OFF)
-    bool fans_paused = false;
+    bool fans_paused; // = false;
     int16_t paused_fanSpeeds[FAN_COUNT] = { 0 };
   #endif
 #endif
 
 // For M0/M1, this flag may be cleared (by M108) to exit the wait-for-user loop
 #if HAS_RESUME_CONTINUE
-  volatile bool wait_for_user = false;
+  volatile bool wait_for_user; // = false;
 #endif
 
 #if HAS_AUTO_REPORTING || ENABLED(HOST_KEEPALIVE_FEATURE)
 #endif
 
 // Inactivity shutdown
-millis_t max_inactive_time = 0,
+millis_t max_inactive_time, // = 0
          stepper_inactive_time = (DEFAULT_STEPPER_DEACTIVE_TIME) * 1000UL;
 
 #ifdef CHDK
-  millis_t chdkHigh = 0;
-  bool chdkActive = false;
+  millis_t chdkHigh; // = 0;
+  bool chdkActive; // = false;
 #endif
 
 #if ENABLED(PID_EXTRUSION_SCALING)

Marlin/src/feature/filwidth.cpp

 
 #include "filwidth.h"
 
-bool filament_sensor = false;                                 // M405/M406 turns filament sensor control ON/OFF.
+bool filament_sensor; // = false;                             // M405/M406 turns filament sensor control ON/OFF.
 float filament_width_nominal = DEFAULT_NOMINAL_FILAMENT_DIA,  // Nominal filament width. Change with M404.
       filament_width_meas = DEFAULT_MEASURED_FILAMENT_DIA;    // Measured filament diameter
 uint8_t meas_delay_cm = MEASUREMENT_DELAY_CM;                 // Distance delay setting

Marlin/src/module/motion.cpp

 XYZ_CONSTS(signed char, home_dir, HOME_DIR);
 
 // Relative Mode. Enable with G91, disable with G90.
-bool relative_mode = false;
+bool relative_mode; // = false;
 
 /**
  * Cartesian Current Position
 
 
 // The active extruder (tool). Set with T<extruder> command.
-uint8_t active_extruder = 0;
+uint8_t active_extruder; // = 0;
 
 // Extruder offsets
 #if HOTENDS > 1