ART: Speed up stack guard page install

Only the main thread doesn't have its stack mapped in under normal
conditions. Reading each page is a lot of overhead and we should
try to avoid it.

Rewrite to first try a (non-fatal) protect. If the outcome is a
success, finish. Otherwise do the stack mapping, and try again.

Bug: 27718174
Change-Id: I16b214567585ed2f09970f618ccdec7eed219fd3