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

Marlin/Marlin_main.cpp

@@ -402,6 +402,10 @@ 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); }
 
+#ifdef SDSUPPORT
+  #include "SdFatUtil.h"
+  int freeMemory() { return SdFatUtil::FreeRam(); }
+#else
   extern "C" {
     extern unsigned int __bss_end;
     extern unsigned int __heap_start;
@@ -418,6 +422,7 @@ extern "C"{
       return free_memory;
     }
   }
+#endif //!SDSUPPORT
 
 //adds an command to the main command buffer
 //thats really done in a non-safe way.