Cleanup the threads check, also resets the CFLAGS and LDFLAGS variables

in cases where no threading library was found.
Submitted by:	Sascha Schumann
Reviewed by:	Ryan Bloom


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@84370 13f79535-47bb-0310-9956-ffa450edef68