Bug 1233863 - ARM64: Avoid BumpSystemStackPointer(). r=sstangl

This function can only handle small immediate adjustments to the stack pointer
because it is not allowed to use scratch registers.

Don't call it from MacroAssembler::Claim() which may allocate large stack
frames. Simply synchronize the system stack pointer to the pseudo stack pointer
instead.

js/src/jit/arm64/vixl/MacroAssembler-vixl.cpp

@@ -1564,11 +1564,14 @@ void MacroAssembler::Claim(const Operand& size) {
     }
   }
 
-  if (!sp.Is(GetStackPointer64())) {
-    BumpSystemStackPointer(size);
-  }
-
   Sub(GetStackPointer64(), GetStackPointer64(), size);
+
+  // Make sure the real stack pointer reflects the claimed stack space.
+  // We can't use stack memory below the stack pointer, it could be clobbered by
+  // interupts and signal handlers.
+  if (!sp.Is(GetStackPointer64())) {
+    Mov(sp, GetStackPointer64());
+  }
 }