build-sys: use m4 quoting consistantly

Change-Id: Ie8c5e15fd9ddf521ac74b07ee0e1252b35e7a816
Reviewed-on: http://gerrit.openafs.org/10008
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>