add OpenBSD platform-support page

Author: semarie

src/doc/rustc/src/platform-support.md

@@ -208,7 +208,7 @@ target | std | host | notes
 `aarch64-unknown-uefi` | * |  | ARM64 UEFI
 `aarch64-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (ILP32 ABI)
 `aarch64-unknown-netbsd` | ✓ | ✓ |
-`aarch64-unknown-openbsd` | ✓ | ✓ | ARM64 OpenBSD
+[`aarch64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | ARM64 OpenBSD
 `aarch64-unknown-redox` | ? |  | ARM64 Redox OS
 `aarch64-uwp-windows-msvc` | ? |  |
 `aarch64-wrs-vxworks` | ? |  |
@@ -237,7 +237,7 @@ target | std | host | notes
 `i686-pc-windows-msvc` | ✓ |  | 32-bit Windows XP support
 `i686-unknown-haiku` | ✓ | ✓ | 32-bit Haiku
 `i686-unknown-netbsd` | ✓ | ✓ | NetBSD/i386 with SSE2
-`i686-unknown-openbsd` | ✓ | ✓ | 32-bit OpenBSD
+[`i686-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 32-bit OpenBSD
 `i686-unknown-uefi` | * |  | 32-bit UEFI
 `i686-uwp-windows-gnu` | ? |  |
 `i686-uwp-windows-msvc` | ? |  |
@@ -272,7 +272,7 @@ target | std | host | notes
 `s390x-unknown-linux-musl` |  |  | S390x Linux (kernel 2.6.32, MUSL)
 `sparc-unknown-linux-gnu` | ✓ |  | 32-bit SPARC Linux
 `sparc64-unknown-netbsd` | ✓ | ✓ | NetBSD/sparc64
-`sparc64-unknown-openbsd` | ? |  |
+[`sparc64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/sparc64
 `thumbv4t-none-eabi` | * |  | ARMv4T T32
 `thumbv7a-pc-windows-msvc` | ? |  |
 `thumbv7a-uwp-windows-msvc` | ✓ |  |
@@ -289,7 +289,7 @@ target | std | host | notes
 [`x86_64-unknown-none`](platform-support/x86_64-unknown-none.md) | * |  | Freestanding/bare-metal x86_64, softfloat
 `x86_64-unknown-none-hermitkernel` | ? |  | HermitCore kernel
 `x86_64-unknown-none-linuxkernel` | * |  | Linux kernel modules
-`x86_64-unknown-openbsd` | ✓ | ✓ | 64-bit OpenBSD
+[`x86_64-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | 64-bit OpenBSD
 `x86_64-unknown-uefi` | * |  | 64-bit UEFI
 `x86_64-uwp-windows-gnu` | ✓ |  |
 `x86_64-uwp-windows-msvc` | ✓ |  |

src/doc/rustc/src/platform-support/openbsd.md

@@ -0,0 +1,56 @@
+# \*-unknown-openbsd
+
+**Tier: 3**
+
+[OpenBSD] multi-platform 4.4BSD-based UNIX-like operating system.
+
+[OpenBSD]: https://www.openbsd.org/
+
+The target names follow this format: `$ARCH-unknown-openbsd`, where `$ARCH` specifies the target processor architecture. The following targets are currently defined:
+
+|          Target name           | C++ library | OpenBSD Platform |
+|--------------------------------|-------------|------------------|
+| `aarch64-unknown-openbsd`      | libc++      | [64-bit ARM systems](https://www.openbsd.org/arm64.html)  |
+| `i686-unknown-openbsd`         | libc++      | [Standard PC and clones based on the Intel i386 architecture and compatible processors](https://www.openbsd.org/i386.html) |
+| `sparc64-unknown-openbsd`      | estdc++     | [Sun UltraSPARC and Fujitsu SPARC64 systems](https://www.openbsd.org/sparc64.html) |
+| `x86_64-unknown-openbsd`       | libc++      | [AMD64-based systems](https://www.openbsd.org/amd64.html) |
+
+Note that all OS versions are *major* even if using X.Y notation (`6.8` and `6.9` are different major versions) and could be binary incompatibles (with breaking changes).
+
+
+## Designated Developers
+
+- [@semarie](https://github.com/semarie), `[email protected]`
+- [lang/rust](https://cvsweb.openbsd.org/cgi-bin/cvsweb/ports/lang/rust/Makefile?rev=HEAD&content-type=text/x-cvsweb-markup) maintainer (see MAINTAINER variable)
+
+Fallback to [email protected], OpenBSD third parties public mailing-list (with openbsd developers readers)
+
+
+## Requirements
+
+These targets are natively compiled and could be cross-compiled.
+C compiler toolchain is required for the purpose of building Rust and functional binaries.
+
+## Building
+
+The target can be built by enabling it for a `rustc` build.
+
+```toml
+[build]
+target = ["$ARCH-unknown-openbsd"]
+
+[target.$ARCH-unknown-openbsd]
+cc = "$ARCH-openbsd-cc"
+```
+
+## Cross-compilation
+
+These targets can be cross-compiled, but LLVM might not build out-of-box.
+
+## Testing
+
+The Rust testsuite could be run natively.
+
+## Building Rust programs
+
+Rust does not yet ship pre-compiled artifacts for these targets.