Fix for a few -Wextra warnings.

Marlin/Marlin_main.cpp

   SERIAL_ERRORLNPGM(MSG_ERR_KILLED);
   LCD_ALERTMESSAGEPGM(MSG_KILLED);
   suicide();
-  while(1); // Wait for reset
+  while(1) { /* Intentionally left empty */ } // Wait for reset
 }
 
 void Stop()

Marlin/Sd2Card.cpp

 /** SPI receive a byte */
 static uint8_t spiRec() {
   SPDR = 0XFF;
-  while (!(SPSR & (1 << SPIF)));
+  while (!(SPSR & (1 << SPIF))) { /* Intentionally left empty */ }
   return SPDR;
 }
 //------------------------------------------------------------------------------
 /** SPI read data - only one call so force inline */
 static inline __attribute__((always_inline))
-  void spiRead(uint8_t* buf, uint16_t nbyte) {
+void spiRead(uint8_t* buf, uint16_t nbyte) {
   if (nbyte-- == 0) return;
   SPDR = 0XFF;
   for (uint16_t i = 0; i < nbyte; i++) {
-    while (!(SPSR & (1 << SPIF)));
+    while (!(SPSR & (1 << SPIF))) { /* Intentionally left empty */ }
     buf[i] = SPDR;
     SPDR = 0XFF;
   }
-  while (!(SPSR & (1 << SPIF)));
+  while (!(SPSR & (1 << SPIF))) { /* Intentionally left empty */ }
   buf[nbyte] = SPDR;
 }
 //------------------------------------------------------------------------------
 /** SPI send a byte */
 static void spiSend(uint8_t b) {
   SPDR = b;
-  while (!(SPSR & (1 << SPIF)));
+  while (!(SPSR & (1 << SPIF))) { /* Intentionally left empty */ }
 }
 //------------------------------------------------------------------------------
 /** SPI send block - only one call so force inline */
   void spiSendBlock(uint8_t token, const uint8_t* buf) {
   SPDR = token;
   for (uint16_t i = 0; i < 512; i += 2) {
-    while (!(SPSR & (1 << SPIF)));
+    while (!(SPSR & (1 << SPIF))) { /* Intentionally left empty */ }
     SPDR = buf[i];
-    while (!(SPSR & (1 << SPIF)));
+    while (!(SPSR & (1 << SPIF))) { /* Intentionally left empty */ }
     SPDR = buf[i + 1];
   }
-  while (!(SPSR & (1 << SPIF)));
+  while (!(SPSR & (1 << SPIF))) { /* Intentionally left empty */ }
 }
 //------------------------------------------------------------------------------
 #else  // SOFTWARE_SPI
   if (cmd == CMD12) spiRec();
 
   // wait for response
-  for (uint8_t i = 0; ((status_ = spiRec()) & 0X80) && i != 0XFF; i++);
+  for (uint8_t i = 0; ((status_ = spiRec()) & 0X80) && i != 0XFF; i++) { /* Intentionally left empty */ }
   return status_;
 }
 //------------------------------------------------------------------------------

Marlin/cardreader.cpp

           SERIAL_PROTOCOLLNPGM(".");
           return;
         }
-        else
-          ;//SERIAL_ECHOLN("dive ok");
+        else
+        {
+          //SERIAL_ECHOLN("dive ok");
+        }
           
         curDir=&myDir; 
         dirname_start=dirname_end+1;
           SERIAL_PROTOCOLLNPGM(".");
           return;
         }
-        else
-          ;//SERIAL_ECHOLN("dive ok");
+        else
+        {
+          //SERIAL_ECHOLN("dive ok");
+        }
           
         curDir=&myDir; 
         dirname_start=dirname_end+1;