Feature/port arm build check (#34)

* add GCC ARM compiler to travis pre-script and add some ARM ports to job

ports/at91sam7s/Makefile

@@ -24,13 +24,10 @@ BACNET_FLAGS += -DMAX_APDU=480
 BACNET_FLAGS += -DCRC_USE_TABLE
 #BACNET_FLAGS += -DDLMSTP_TEST
 
-BACNET_CORE = ../../src
+BACNET_SRC = ../../src
+BACNET_CORE = $(BACNET_SRC)/bacnet
 BACNET_BASIC = $(BACNET_CORE)/basic
-BACNET_INCLUDE = $(BACNET_CORE)
-INCLUDES = -I.
-INCLUDES += -I$(BACNET_INCLUDE)
-INCLUDES += -I$(BACNET_OBJECT)
-INCLUDES += -I$(BACNET_HANDLER)
+INCLUDES = -I. -I$(BACNET_SRC)
 #OPTIMIZATION = -O0
 OPTIMIZATION = -Os
 CFLAGS = -fno-common $(INCLUDES) $(BACNET_FLAGS) -Wall -g
@@ -100,7 +97,6 @@ CORESRC = $(BACNET_CORE)/abort.c \
 	$(BACNET_CORE)/reject.c \
 	$(BACNET_CORE)/rp.c \
 	$(BACNET_CORE)/rpm.c \
-	$(BACNET_CORE)/version.c \
 	$(BACNET_CORE)/whohas.c \
 	$(BACNET_CORE)/whois.c \
 	$(BACNET_CORE)/wp.c

ports/at91sam7s/rs485.c

@@ -32,7 +32,7 @@
 #include <stdbool.h>
 #include <stdlib.h>
 #include <stdio.h>
-#include "bacnet/basic/sys/mstimer.h"
+#include "timer.h"
 
 /* This file has been customized for use with UART0
    on the AT91SAM7S-EK */

ports/at91sam7s/timer.c

@@ -43,6 +43,7 @@
 #include <stdint.h>
 #include "board.h"
 #include "bacnet/datalink/dlmstp.h"
+#include "timer.h"
 
 /* global variable counts interrupts */
 volatile unsigned long Timer_Milliseconds;
@@ -309,8 +310,10 @@ static void Timer0IrqHandler(
     dummy = pTC->TC_SR;
     /* increment the tick count */
     Timer_Milliseconds++;
-    if (SilenceTime < 60000)
+    if (SilenceTime < 60000) {
         SilenceTime++;
+    }
+    (void)dummy;
 }
 
 int Timer_Silence(