configure: Fix detection whether libcurl is linked against gnutls
configure: Fix detection whether libcurl is linked against gnutls

The find_curl macro is also checking whether libcurl is linked against
gnutls. However the check depends on "CURL_LIBS" which wasn't defined
by the macro.

This commit will define "CURL_LIBS" so that the check works as expected.

p0pr0ck5/ModSecurity,bjh7242/ModSecurity,csanders-git/ModSecurity,marcstern/ModSecurity,bjh7242/ModSecurity,p0pr0ck5/ModSecurity,csanders-git/ModSecurity,p0pr0ck5/ModSecurity,p0pr0ck5/ModSecurity,csanders-git/ModSecurity,marcstern/ModSecurity,bjh7242/ModSecurity,bjh7242/ModSecurity,marcstern/ModSecurity,csanders-git/ModSecurity,marcstern/ModSecurity,marcstern/ModSecurity,irtnog/ModSecurity,p0pr0ck5/ModSecurity,irtnog/ModSecurity,csanders-git/ModSecurity,bjh7242/ModSecurity,irtnog/ModSecurity,phpModSecurity/ModSecurity,csanders-git/ModSecurity,bjh7242/ModSecurity,p0pr0ck5/ModSecurity,irtnog/ModSecurity,irtnog/ModSecurity,irtnog/ModSecurity