RFR: 8221149: os::malloc checks MallocCatchPtr outside of ifdef ASSERT block

[Stefan Karlsson]

Hi all,

Please review this patch to move the MallocCatchPtr check into the ifdef 
ASSERT block, just like the other usages of it.

http://cr.openjdk.java.net/~stefank/8221149/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8221149

A side note: Is the intention that MallocCatchPtr should find pointers 
to the memory address returned from ::malloc, or the memory address we 
hand out from os::malloc? Currently it's the latter and it's not obvious 
from the the code if this was the intention from the beginning.

  704   // Wrap memory with guard
  705   GuardedMemory guarded(ptr, size + nmt_header_size);
  706   ptr = guarded.get_user_ptr();
  707
  708   if ((intptr_t)ptr == (intptr_t)MallocCatchPtr) {

Thanks,
StefanK