[build-support] fix on enable_devtoolset_inner.sh, take two
[build-support] fix on enable_devtoolset_inner.sh, take two

Prior to this fix, when configuring a build via cmake as described at
https://kudu.apache.org/docs/installation.html#build_from_source,
the following error was output (at least by bash 4.1.2):

  build-support/enable_devtoolset_inner.sh: line 28: [: too many arguments

This is a follow-up to 719418a60235a5155efe95c37e9fc6e319f41e0c.

Change-Id: I8de79a99a5386e47e968ca9e8f6939159b06fbda
Reviewed-on: http://gerrit.cloudera.org:8080/14825
Tested-by: Kudu Jenkins
Reviewed-by: Andrew Wong <b68e4fdc6430321a6b47400732ff97d7ae91234e@cloudera.com>

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu