ART: Generate path to entrypoints in VisitLoadString for x86

Code size unmeasured, presumably ~-1%.

Generate code to go into string dex cache entrypoints in VisitLoadString
instead of with slow paths, since we now go into entrypoints almost
every time.

Change-Id: Ic4335a23934547737dbda12111f672da1e6c0ef7
Tests: test-art-host CC baker
1 file changed