Makefile: Redone

+ Removed most explicit pathnames, use the standard make "VPATH" to let
make find the files for itself.

+ Added a "hardware variant" variable that allows compiging Sanguino and
Gen7 as well as "generic" arduino.

+ Allows overriding the MOTHERBOARD define from the Makefile

+ Removed the 'preprocessor' bit that wasn't needed, now just "include" the
files that are needed, since it allows gcc to show the right file/line
when displaying error/warnings.

+ Uses gcc's own dependency generator to generate the .d files, and
and include these instead of self-patching the makefile

Signed-off-by: Michel Pollet <buserror@gmail.com>

Marlin/Configuration.h

@@ -29,7 +29,9 @@
 // Ultimaker = 7
 // Teensylu = 8
 // Gen3+ =9
+#ifndef MOTHERBOARD
 #define MOTHERBOARD 7
+#endif
 
 //===========================================================================
 //=============================Thermal Settings  ============================
@@ -193,7 +195,7 @@ const bool Z_ENDSTOPS_INVERTING = true; // set to true to invert the logic of th
 //#define ULTRA_LCD  //general lcd support, also 16x2
 //#define SDSUPPORT // Enable SD Card Support in Hardware Console
 
-#define ULTIPANEL
+//#define ULTIPANEL
 #ifdef ULTIPANEL
 //  #define NEWPANEL  //enable this if you have a click-encoder panel
   #define SDSUPPORT