Continued work configuring nix flakes

pcap-sys/build.rs

@@ -14,7 +14,7 @@
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 fn main() {
-    let dst = cmake::Config::new("libpcap")
+    let dst = cmake::Config::new(std::env!("SPARSE_BUILD_LIBPCAP"))
         .define("BUILD_SHARED_LIBS", "OFF")
         .define("BUILD_WITH_LIBNL", "OFF")
         .define("DISABLE_BLUETOOTH", "ON")