Check Dragonfly BSD and OpenBSD in CI

Build, but don't test, for these operating systems.  Thanks to
@rtzoeller for the tip.

Also, fix the OpenBSD build.

Author: asomers

.cirrus.yml

@@ -10,13 +10,14 @@ env:
   TOOL: cargo
   # The MSRV
   TOOLCHAIN: 1.46.0
+  ZFLAGS:
 
 # Tests that don't require executing the build binaries
 build: &BUILD
   build_script:
     - . $HOME/.cargo/env || true
-    - $TOOL +$TOOLCHAIN $BUILD --target $TARGET --all-targets
-    - $TOOL +$TOOLCHAIN doc --no-deps --target $TARGET
+    - $TOOL +$TOOLCHAIN $BUILD $ZFLAGS --target $TARGET --all-targets
+    - $TOOL +$TOOLCHAIN doc $ZFLAGS --no-deps --target $TARGET
 
 # Tests that do require executing the binaries
 test: &TEST
@@ -226,6 +227,26 @@ task:
   << : *BUILD
   before_cache_script: rm -rf $CARGO_HOME/registry/index
 
+# Rust Tier 3 targets can't use Rustup
+task:
+  container:
+    image: rustlang/rust:nightly
+  env:
+    BUILD: check
+    TOOLCHAIN: nightly
+    ZFLAGS: -Zbuild-std
+  matrix:
+    - name: DragonFly BSD x86_64
+      env:
+        TARGET: x86_64-unknown-dragonfly
+    - name: OpenBSD x86_64
+      env:
+        TARGET: x86_64-unknown-openbsd
+  setup_script:
+    - rustup component add rust-src
+  << : *BUILD
+  before_cache_script: rm -rf $CARGO_HOME/registry/index
+
 # Test that we can build with the lowest version of all dependencies.
 # "cargo test" doesn't work because some of our dev-dependencies, like
 # rand, can't build with their own minimal dependencies.

README.md

@@ -79,8 +79,10 @@ Tier 2:
 
 Tier 3:
   * x86_64-fuchsia
-  * x86_64-unknown-redox
+  * x86_64-unknown-dragonfly
   * x86_64-unknown-linux-gnux32
+  * x86_64-unknown-openbsd
+  * x86_64-unknown-redox
 
 ## Usage
 

bors.toml

@@ -4,6 +4,7 @@ status = [
   "Android armv7",
   "Android i686",
   "Android x86_64",
+  "DragonFly BSD x86_64",
   "FreeBSD amd64 & i686",
   "Fuchsia x86_64",
   "Linux MIPS",
@@ -25,6 +26,7 @@ status = [
   "Linux x86_64",
   "Minver",
   "NetBSD x86_64",
+  "OpenBSD x86_64",
   "OSX x86_64",
   "Redox x86_64",
   "Rust Stable",

src/sys/resource.rs

@@ -49,7 +49,11 @@ libc_enum! {
         ), repr(i32))]
     #[non_exhaustive]
     pub enum Resource {
-        #[cfg(not(any(target_os = "netbsd", target_os = "freebsd")))]
+        #[cfg(not(any(
+                    target_os = "freebsd",
+                    target_os = "netbsd",
+                    target_os = "openbsd"
+        )))]
         /// The maximum amount (in bytes) of virtual memory the process is
         /// allowed to map.
         RLIMIT_AS,