Add experimental flag to support OpenJDK builds.

bug: 8992787

(cherry picked from commit d1dbe7f5a23bacdff086b4992e1d31a96da706c3)

Conflicts:
	core/main.mk

Change-Id: Ie977d4f26ae8d3eee9d7b9cf2c0c270bee5b54b3

Conflicts:
	core/combo/javac.mk
	core/main.mk