Add Build-Only CI for OpenBSD, Dragonfly, and Haiku

Signed-off-by: Joe Richey <joerichey@google.com>

.github/workflows/tests.yml

@@ -319,6 +319,12 @@ jobs:
         run: cargo build -Z build-std=core --target=aarch64-kmc-solid_asp3
       - name: Nintendo 3DS
         run: cargo build -Z build-std=core --target=armv6k-nintendo-3ds
+      - name: OpenBSD
+        run: cargo build -Z build-std=std --target=x86_64-unknown-openbsd --features=std
+      - name: Dragonfly BSD
+        run: cargo build -Z build-std=std --target=x86_64-unknown-dragonfly --features=std
+      - name: Haiku OS
+        run: cargo build -Z build-std=std --target=x86_64-unknown-haiku --features=std
 
   clippy-fmt:
     name: Clippy + rustfmt

src/openbsd.rs

@@ -8,6 +8,7 @@
 
 //! Implementation for OpenBSD
 use crate::{util_libc::last_os_error, Error};
+use core::mem::MaybeUninit;
 
 pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
     // getentropy(2) was added in OpenBSD 5.6, so we can use it unconditionally.