CI: add OpenBSD compilation check (signal11#449)

NOTES, as described in signal11#31:
- it is still hard to use HIDAPI on OpenBSD since it is hard to use LIBUSB with HID devices;
- there is a name colision with `hid_init` from `usbhid` OpenBSD library;

Author: Youw

.builds/openbsd.yml

@@ -0,0 +1,19 @@
+image: openbsd/latest
+packages:
+- cmake
+- pkgconf
+- libusb1--
+- libiconv
+- ninja
+sources:
+- https://github.com/libusb/hidapi
+tasks:
+- setup: |
+    cd hidapi
+    mkdir -p build install
+    cmake -GNinja -B build -S . -DCMAKE_INSTALL_PREFIX=install
+- build: |
+    cd hidapi/build
+    ninja
+    ninja install
+    ninja clean