Introduce a V8_NORETURN macro and use it to make GCC 4.9.2 happy again.

src/heap/spaces-inl.h

Index: src/heap/spaces-inl.h
diff --git a/src/heap/spaces-inl.h b/src/heap/spaces-inl.h
index 8dca9b198beaaf39c6b6256630b4fe37b1d7703c..8e99739d5f21113e4ea7885fdc25b57095a47edf 100644
--- a/src/heap/spaces-inl.h
+++ b/src/heap/spaces-inl.h
@@ -446,7 +446,7 @@ AllocationResult NewSpace::AllocateRawAligned(int size_in_bytes,
 
 AllocationResult NewSpace::AllocateRawUnaligned(int size_in_bytes) {
   Address top = allocation_info_.top();
-  if (allocation_info_.limit() - top < size_in_bytes) {
+  if (allocation_info_.limit() < top + size_in_bytes) {
     // See if we can create room.
     if (!EnsureAllocation(size_in_bytes, kWordAligned)) {
       return AllocationResult::Retry();