Follow up to r1535027 and r1535157:

Fix sed re escaping issue in recognition of Linux kernel version.

PR: 55690
Submitted by: Arfrever Frehtes Taifersar Arahesis <arfrever.fta gmail.com>
Reviewed by: trawick


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1541486 13f79535-47bb-0310-9956-ffa450edef68