Align libgloss/arm and libc/sys/arm sources: HeapInfo and __heap_limit

Applied changes from commit 8d98f95:

	* arm/crt0.S: Initialise __heap_limit when ARM_RDI_MONITOR is defined.
	* arm/syscalls.c: define __heap_limit global symbol.
	* arm/syscalls.c (_sbrk): Honour __heap_limit.

Applied changes from commit 8d98f95:
	Fixed semihosting for ARM when heapinfo not provided by debugger

newlib/libc/sys/arm/crt0.S

@@ -282,6 +282,13 @@
 #endif
 	ldr	r0, .LC0	/*  Point at values read.  */
 
+	/* Set __heap_limit.  */
+	ldr     r1, [r0, #4]
+	cmp     r1, #0
+	beq     .LC33
+	ldr     r2, =__heap_limit
+	str     r1, [r2]
+.LC33:
 	ldr     r1, [r0, #0]
 	cmp     r1, #0
 	bne     .LC32

newlib/libc/sys/arm/syscalls.c

@@ -487,6 +487,9 @@ _getpid (void)
   return (pid_t)1;
 }
 
+/* Heap limit returned from SYS_HEAPINFO Angel semihost call.  */
+uint __heap_limit = 0xcafedead;
+
 void * __attribute__((weak))
 _sbrk (ptrdiff_t incr)
 {
@@ -499,7 +502,9 @@ _sbrk (ptrdiff_t incr)
 
   prev_heap_end = heap_end;
 
-  if (heap_end + incr > stack_ptr)
+  if ((heap_end + incr > stack_ptr)
+      /* Honour heap limit if it's valid.  */
+      || (__heap_limit != 0xcafedead && heap_end + incr > (char *)__heap_limit))
     {
       /* Some of the libstdc++-v3 tests rely upon detecting
 	 out of memory errors, so do not abort here.  */