Define HAVE_KERN_PROC on FreeBSD to fix rust-lang/rust#54434 (#294)

* Define HAVE_KERN_PROC on FreeBSD to fix rust-lang/rust#54434

For the same reason define HAVE_KERN_PROC_ARGS on NetBSD.

This depends on having [1] available in libbacktrace.

[1] ianlancetaylor/libbacktrace@0f06cda

* Add dragonfly too

Author: Tobias Kortkamp

crates/backtrace-sys/build.rs

@@ -72,6 +72,12 @@ fn main() {
     File::create(out_dir.join("config.h")).unwrap();
     if target.contains("android") {
         maybe_enable_dl_iterate_phdr_android(&mut build);
+    } else if target.contains("dragonfly") || target.contains("freebsd") {
+        build.define("HAVE_DL_ITERATE_PHDR", "1");
+        build.define("HAVE_KERN_PROC", "1");
+    } else if target.contains("netbsd") {
+        build.define("HAVE_DL_ITERATE_PHDR", "1");
+        build.define("HAVE_KERN_PROC_ARGS", "1");
     } else if !target.contains("apple-ios")
         && !target.contains("solaris")
         && !target.contains("redox")