PR14957: Don't force __GFP_ZERO into kmalloc_node

PR14957: Don't force __GFP_ZERO into kmalloc_node

It turns out that rhel5-era kernels have a BUG check in slab cache_grow
that doesn't permit __GFP_ZERO from this path.  Later kernels corrected
this, as the implementation of kzalloc_node is just kmalloc_node with
__GFP_ZERO added, but for compatibility we can't rely on that.

* runtime/linux/alloc.c (_stp_kzalloc_node_gfp): Use a plain
  _stp_kmalloc_node_gfp, then memset-0 manually.