avoid error if bazel intermediates dir already exists

Previously, the build failed if the directory already existed,
so mixed builds had to be null builds.

Test: lunch aosp_flame && USE_BAZEL=1 USE_BAZEL_ANAYSIS=1 m libc &&
  USE_BAZEL=1 USE_ANALYSIS=1 m libc
Change-Id: I167cb82b3e47e9388a1ebca7daffe45f91474125