cmake: improved to use libraries provided by the system as much ass possible

develop/cmake/cmake.conf

@@ -25,3 +25,14 @@ hook_add preconf 9 'cmake_preconf'
 configscript="../configure"
 
 confopt="--prefix=$root/$prefix"
+
+# first try to use all system-installed third-party libraries
+var_append confopt ' ' "--system-libs"
+
+# use cmake-provided libraries if they are not available on the system
+for x in curl expat zlib bzip2 libarchive ; do
+	if ! pkginstalled -f $x; then
+		echo_status "Using cmake-provided $x (not available on the system)"
+		var_append confopt ' ' "--no-system-$x"
+	fi
+done