Build: Support for compiled-classes file

Allow a compiled-classes file for pre-opting.

Bug: 18410571

(cherry picked from commit 4fec0bb265ac8cdbe883b8868abfcb56713db170)

Change-Id: I8c69dd0fb8c04aaae0c4f062049cc9cce7d755c7

Conflicts:
	core/dex_preopt_libart.mk
	core/dex_preopt_libart_boot.mk