This copies the AC_SEARCH_LIBS check from the main strongSwan
configure.ac.
When building networkmanager-strongswan with slibtool if fails.
ld: cannot find none: No such file or directory
ld: cannot find required: No such file or directory
This is because configure.ac uses AC_SEARCH_LIBS to find dlopen which
sets the value of $ac_cv_search_dlopen to 'none required' which then
gets set in DL_LIBS and passed to slibtool.
With GNU libtool it silently ignores the unknown arguments.
Gentoo issue: https://bugs.gentoo.org/914100Closesstrongswan/strongswan#2141
Signed-off-by: orbea <[email protected]>
