Prepare for move to prebuilts/build-tools

The prebuilt is moving from prebuilts/misc to prebuilts/build-tools so
that it will actually get updates. Ensure that it's always using a
matched data directory, instead of external/bison.

Test: bison --print-datadir
Change-Id: Id0b90054a158c90d22f875e922081edb44fb4b57
1 file changed