vold: restore -D__ANDROID_DEBUGGABLE__

Regression introduced by
commit 7ebcc2bcfde2cf6713e2975224034b06ba0943d8
("Revert "[Vold] Conditional dependency to ARC++ ObbVolume"")
errantly removed the product_variables support for
-D__ANDROID_DEBUGGABLE__ when built for userdebug builds.

Restore stanza.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 161454607
Test: adb-remount-test no longer reports a problem
Change-Id: Ia7e55d1174fa7fac2d934d4aac06d15e8be388af
1 file changed