Work around a GCC bug, producing this code:

  unsigned char *llvm_cbe_X;
...
  llvm_cbe_X = 0; *((void**)&llvm_cbe_X) = __builtin_stack_save();

instead of:

  llvm_cbe_X = __builtin_stack_save();

See PR1809 for details.

llvm-svn: 44415