fix whitespace errors in acinclude.m4

Use tabs instead of spaces in the sysname lookup case
statement for the macos cases.

Reviewed-on: http://gerrit.openafs.org/11566
Reviewed-by: D Brashear <shadow@your-file-system.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit 7ae5b73a90940fe693fd5a726aa31408bd7aec39)

Change-Id: I2860cd835242f0972b8795f2f7fedcb012aa18ea
Reviewed-on: http://gerrit.openafs.org/11611
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>