ARM: get sermsg.c/.h in.

Compiled flawlessly, ran all test flawlessly, and at the end it
turned out mendel.c had an obsolete #include. Very nice.

Makefile-ARM

@@ -97,7 +97,7 @@ TARGET = $(PROGRAM).hex
 #SOURCES = $(wildcard *.c)
 # Until the generic ARM port is completed, we'd have to wrap all sources
 # in #ifdef __AVR__. To avoid this, build only a selection for now:
-SOURCES  = mendel.c cpu.c serial.c
+SOURCES  = mendel.c cpu.c serial.c sermsg.c
 SOURCES += mbed-pinmap.c
 ifeq ($(MCU), lpc1114)
   SOURCES += mbed-system_LPC11xx.c

mendel.c

@@ -38,7 +38,6 @@
 #include	"gcode_parse.h"
 #include	"timer.h"
 #include	"temp.h"
-#include	"sermsg.h"
 #include	"watchdog.h"
 #include	"debug.h"
 #include	"sersendf.h"