Add C++ support to Makefile, and proof-of-concept simple.cpp example

This is a work in progress based on @mikejac's work.

Missing:
* No 'new' operator.
* I don't think STL is currently supported.

FreeRTOS/Source/portable/esp8266/port.c

@@ -178,6 +178,9 @@ void xPortSysTickHandle (void)
 	//OpenNMI();
 }
 
+static bool sdk_compat_initialised;
+void sdk_compat_initialise(void);
+
 /*
  * See header file for description.
  */
@@ -186,6 +189,14 @@ portBASE_TYPE xPortStartScheduler( void )
     _xt_isr_attach(INUM_SOFT, SV_ISR);
     _xt_isr_unmask(BIT(INUM_SOFT));
 
+    /* ENORMOUS HACK: Call the sdk_compat_initialise() function.
+       This can be removed happily once we have open source startup code.
+    */
+    if(!sdk_compat_initialised) {
+        sdk_compat_initialised = true;
+        sdk_compat_initialise();
+    }
+
     /* Initialize system tick timer interrupt and schedule the first tick. */
     sdk__xt_tick_timer_init();