Don't automatically link to libpcap

pkg-config's default config will output `rustc-link-lib` when it finds a
package. However, per this project's readme, linkage is the
responsibility of the user, so it seems like merely probing for the
version should not change any subsequent build config.

Lines previously present in build.rs output that are now gone:

```
[pcap 2.3.0] cargo:rustc-link-search=native=/usr/lib/x86_64-linux-gnu
[pcap 2.3.0] cargo:rustc-link-lib=pcap
```

Similarly, the `#[link(name = "pcap")]` in `raw` was making dependent
binaries automatically link to libpcap.so.

Author: marshallpierce

build.rs

@@ -197,6 +197,7 @@ fn main() {
 
 fn from_pkg_config() -> Result<pkg_config::Library, pkg_config::Error> {
     let mut config = pkg_config::Config::new();
+    config.cargo_metadata(false);
     // If the user has went out of their way to specify LIBPCAP_VER (even though
     // LIBCAP_LIBDIR wasn't set), respect it. Otherwise fall back to any version
     // as long as it's supported.

examples/easylisten.rs

@@ -1,3 +1,6 @@
+#[path = "helpers/link.rs"]
+mod link;
+
 fn main() {
     // get the default Device
     let device = pcap::Device::lookup()

examples/getdevices.rs

@@ -1,3 +1,6 @@
+#[path = "helpers/link.rs"]
+mod link;
+
 fn main() {
     // list all of the devices pcap tells us are available
     for device in pcap::Device::list().expect("device lookup failed") {

examples/getstatistics.rs

@@ -1,3 +1,6 @@
+#[path = "helpers/link.rs"]
+mod link;
+
 fn main() {
     // get the default Device
     let device = pcap::Device::lookup()

examples/helpers/link.rs

@@ -0,0 +1,9 @@
+//! Trigger linking against the appropriate library for example binaries.
+
+#[cfg(not(windows))]
+#[link(name = "pcap")]
+extern "C" {}
+
+#[cfg(windows)]
+#[link(name = "wpcap")]
+extern "C" {}

examples/iterprint.rs

@@ -2,6 +2,9 @@
 use pcap::{Capture, Device, Packet, PacketCodec, PacketHeader};
 use std::error;
 
+#[path = "helpers/link.rs"]
+mod link;
+
 /// Represents a owned packet
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct PacketOwned {

examples/lendingiterprint.rs

@@ -4,6 +4,9 @@ use std::error;
 
 use gat_std::gatify;
 
+#[path = "helpers/link.rs"]
+mod link;
+
 #[gatify]
 fn main() -> Result<(), Box<dyn error::Error>> {
     let device = Device::lookup()?.ok_or("no device available")?;

examples/listenlocalhost.rs

@@ -1,3 +1,6 @@
+#[path = "helpers/link.rs"]
+mod link;
+
 fn main() {
     // listen on the device named "any", which is only available on Linux. This is only for
     // demonstration purposes.

examples/loop.rs

@@ -1,3 +1,6 @@
+#[path = "helpers/link.rs"]
+mod link;
+
 fn main() {
     // get the default Device
     let device = pcap::Device::lookup()

examples/nfbpfcompile.rs

@@ -7,6 +7,9 @@ use pcap::{BpfProgram, Capture, Linktype};
 use std::env;
 use std::process;
 
+#[path = "helpers/link.rs"]
+mod link;
+
 fn main() {
     let (layertype, prog) = match env::args().len() {
         2 => ("RAW".to_string(), env::args().nth(1).unwrap()),