Android o preview 4
Do not abort when assemble_vintf does not get env vars

Make reasonable defaults when env vars are missing, so that
new flags added won't cause a build breakage on old branches.

Test: builds (assemble_vintf is used only at build time)
Bug: 38325029
Change-Id: Ib76f321ee0de8939b24313e6b123d1b2d14a1e8d
1 file changed