perchild MPM: Fix thread safety problem in the use of longjmp().

Submitted by:   Tsuyoshi SASAMOTO <nazonazo super.win.ne.jp>
Reviewed by:	Jeff Trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@104436 13f79535-47bb-0310-9956-ffa450edef68