Various fixes for compiler warnings

add BLTouch-related messages in english and (rusty) french;
add missing endstops.h in ultralcd.cpp;
fix misc. compiler warnings;
fix lsf_reset - ZERO macro can't handle a pointer as it would only memset the size of the pointer, not the size of the entire struct

Marlin/Marlin_main.cpp

      */
     #if ENABLED(BLTOUCH_HEATERS_OFF)
 
-      bool set_heaters_for_bltouch(const bool deploy) {
+      void set_heaters_for_bltouch(const bool deploy) {
         static bool heaters_were_disabled = false;
         static millis_t next_emi_protection;
         static float temps_at_entry[HOTENDS];

Marlin/language_en.h

 #ifndef MSG_BLTOUCH_RESET
   #define MSG_BLTOUCH_RESET                   _UxGT("Reset BLTouch")
 #endif
+#ifndef MSG_BLTOUCH_DEPLOY
+  #define MSG_BLTOUCH_DEPLOY                  _UxGT("Deploy BLTouch")
+#endif
+#ifndef MSG_BLTOUCH_STOW
+  #define MSG_BLTOUCH_STOW                    _UxGT("Stow BLTouch")
+#endif
 #ifndef MSG_HOME
   #define MSG_HOME                            _UxGT("Home") // Used as MSG_HOME " " MSG_X MSG_Y MSG_Z " " MSG_FIRST
 #endif

Marlin/language_fr.h

 #define MSG_ZPROBE_OUT                      _UxGT("Z sonde extè. lit")
 #define MSG_BLTOUCH_SELFTEST                _UxGT("Autotest BLTouch")
 #define MSG_BLTOUCH_RESET                   _UxGT("RaZ BLTouch")
+#define MSG_BLTOUCH_DEPLOY                  _UxGT("Déployer BLTouch")
+#define MSG_BLTOUCH_STOW                    _UxGT("Ranger BLTouch")
 #define MSG_HOME                            _UxGT("Origine")  // Used as MSG_HOME " " MSG_X MSG_Y MSG_Z " " MSG_FIRST
 #define MSG_FIRST                           _UxGT("Premier")
 #define MSG_ZPROBE_ZOFFSET                  _UxGT("Décalage Z")

Marlin/least_squares_fit.cpp

 
 #include "least_squares_fit.h"
 
-void incremental_LSF_reset(struct linear_fit_data *lsf) { ZERO(lsf); }
+void incremental_LSF_reset(struct linear_fit_data *lsf) {
+  memset(lsf, 0, sizeof(linear_fit_data));
+}
 
 void incremental_LSF(struct linear_fit_data *lsf, float x, float y, float z) {
   lsf->xbar += x;

Marlin/ultralcd.cpp

   #include "duration_t.h"
 #endif
 
+#if ENABLED(BLTOUCH)
+  #include "endstops.h"
+#endif
+
 int lcd_preheat_hotend_temp[2], lcd_preheat_bed_temp[2], lcd_preheat_fan_speed[2];
 
 #if ENABLED(FILAMENT_LCD_DISPLAY) && ENABLED(SDSUPPORT)