RFR: 8186780: clang-4.0 fastdebug assertion failure in os_linux_x86:os::verify_stack_alignment()

[Martin Buchholz]

I see stack pointers (and frame pointers) declared as intptr_t* which makes
no sense to me.  These are all "just" pointers, so declare them as either
void* or intptr_t or address

In the construct below, we could elide the cast if we had declared esp
right in the first place?!

  intptr_t* esp;
  __asm__ __volatile__ ("mov %%"SPELL_REG_SP", %0":"=r"(esp):);
  return (address) esp;