Use SdFatUtil::FreeRam() for freeMemory() if there

Marlin/Marlin_main.cpp

@@ -402,22 +402,27 @@ void serial_echopair_P(const char *s_P, double v)
 void serial_echopair_P(const char *s_P, unsigned long v)
     { serialprintPGM(s_P); SERIAL_ECHO(v); }
 
-extern "C"{
-  extern unsigned int __bss_end;
-  extern unsigned int __heap_start;
-  extern void *__brkval;
+#ifdef SDSUPPORT
+  #include "SdFatUtil.h"
+  int freeMemory() { return SdFatUtil::FreeRam(); }
+#else
+  extern "C" {
+    extern unsigned int __bss_end;
+    extern unsigned int __heap_start;
+    extern void *__brkval;
 
-  int freeMemory() {
-    int free_memory;
+    int freeMemory() {
+      int free_memory;
 
-    if((int)__brkval == 0)
-      free_memory = ((int)&free_memory) - ((int)&__bss_end);
-    else
-      free_memory = ((int)&free_memory) - ((int)__brkval);
+      if ((int)__brkval == 0)
+        free_memory = ((int)&free_memory) - ((int)&__bss_end);
+      else
+        free_memory = ((int)&free_memory) - ((int)__brkval);
 
-    return free_memory;
+      return free_memory;
+    }
   }
-}
+#endif //!SDSUPPORT
 
 //adds an command to the main command buffer
 //thats really done in a non-safe way.