configure: Bugfix (#8413)

commit 429d14d4 introduced
TF_BAZEL_TARGETS. However, it turns out that if:

TF_BAZEL_TARGETS="//tensorflow/... -//tensorflow/contrib/nccl/..."
then
bazel fetch "$TF_BAZEL_TARGETS"
work out fine, but
bazel fetch $TF_BAZEL_TARGETS
fails with
"Invalid options syntax: -//tensorflow/contrib/nccl/...

However, if
TF_BAZEL_TARGETS="//tensorflow:libtensorflow.so //tensorflow/tools/lib_packages:clicences_generate"
then
bazel fetch "$TF_BAZEL_TARGETS"
fails with:
  ERROR: Error while parsing 'deps(//tensorflow:libtensorflow.so  //tensorflow/tools/lib_packages:clicences_generate)'
while
bazel fetch $TF_BAZEL_TARGETS
succeeds.

The latter is used in the Windows libtensorflow release scripts.
For now, a quick fix to make the intended usage of TF_BAZEL_TARGETS
work. Revisit the appropriate fix later.