Improve the m4 detection of cgal
Description
Use LIBS instead of LDFLAGS to make sure they come at the end of the link line which is important for the header-only version.
Moreover, --with-cgal=no disables the check now. Also don't check all the different folders - either it is CGAL_HOME, or given by --with-cgal or it is in the system folders. We don't need to cover anything else.
Also use AC_LINK_IFELSE instead of AC_RUN_IFELSE because it is also fine for cross compiling - here we don't really need to run the code; as long as it links, it is fine.