Add platform docs for FreeBSD.

Author: asomers

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

@@ -100,7 +100,7 @@ target | notes
 [`riscv64gc-unknown-linux-gnu`](platform-support/riscv64gc-unknown-linux-gnu.md) | RISC-V Linux (kernel 4.20, glibc 2.29)
 [`riscv64gc-unknown-linux-musl`](platform-support/riscv64gc-unknown-linux-musl.md) | RISC-V Linux (kernel 4.20, musl 1.2.3)
 [`s390x-unknown-linux-gnu`](platform-support/s390x-unknown-linux-gnu.md) | S390x Linux (kernel 3.2, glibc 2.17)
-`x86_64-unknown-freebsd` | 64-bit FreeBSD
+[`x86_64-unknown-freebsd`](platform-support/freebsd.md) | 64-bit FreeBSD
 `x86_64-unknown-illumos` | illumos
 `x86_64-unknown-linux-musl` | 64-bit Linux with musl 1.2.3
 [`x86_64-unknown-netbsd`](platform-support/netbsd.md) | NetBSD/amd64
@@ -166,7 +166,7 @@ target | std | notes
 `i586-unknown-linux-musl` | ✓ | 32-bit Linux w/o SSE, musl 1.2.3 [^x86_32-floats-x87]
 [`i686-linux-android`](platform-support/android.md) | ✓ | 32-bit x86 Android [^x86_32-floats-return-ABI]
 [`i686-pc-windows-gnullvm`](platform-support/pc-windows-gnullvm.md) | ✓ | 32-bit x86 MinGW (Windows 10+), LLVM ABI [^x86_32-floats-return-ABI]
-`i686-unknown-freebsd` | ✓ | 32-bit FreeBSD [^x86_32-floats-return-ABI]
+[`i686-unknown-freebsd`](platform-support/freebsd.md) | ✓ | 32-bit FreeBSD [^x86_32-floats-return-ABI]
 `i686-unknown-linux-musl` | ✓ | 32-bit Linux with musl 1.2.3 [^x86_32-floats-return-ABI]
 [`i686-unknown-uefi`](platform-support/unknown-uefi.md) | ? | 32-bit UEFI
 [`loongarch64-unknown-none`](platform-support/loongarch-none.md) | * | LoongArch64 Bare-metal (LP64D ABI)
@@ -258,7 +258,7 @@ target | std | host | notes
 [`aarch64-unknown-teeos`](platform-support/aarch64-unknown-teeos.md) | ? |  | ARM64 TEEOS |
 [`aarch64-unknown-nto-qnx700`](platform-support/nto-qnx.md) | ? |  | ARM64 QNX Neutrino 7.0 RTOS |
 [`aarch64-unknown-nto-qnx710`](platform-support/nto-qnx.md) | ✓ |  | ARM64 QNX Neutrino 7.1 RTOS |
-`aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
+[`aarch64-unknown-freebsd`](platform-support/freebsd.md) | ✓ | ✓ | ARM64 FreeBSD
 [`aarch64-unknown-hermit`](platform-support/hermit.md) | ✓ |  | ARM64 Hermit
 `aarch64-unknown-illumos` | ✓ | ✓ | ARM64 illumos
 `aarch64-unknown-linux-gnu_ilp32` | ✓ | ✓ | ARM64 Linux (ILP32 ABI)
@@ -277,14 +277,14 @@ target | std | host | notes
 `armv4t-unknown-linux-gnueabi` | ? |  | Armv4T Linux
 [`armv5te-none-eabi`](platform-support/armv5te-none-eabi.md) | * |  | Bare Armv5TE
 `armv5te-unknown-linux-uclibceabi` | ? |  | Armv5TE Linux with uClibc
-`armv6-unknown-freebsd` | ✓ | ✓ | Armv6 FreeBSD
+[`armv6-unknown-freebsd`](platform-support/freebsd.md) | ✓ | ✓ | Armv6 FreeBSD
 [`armv6-unknown-netbsd-eabihf`](platform-support/netbsd.md) | ✓ | ✓ | Armv6 NetBSD w/hard-float
 [`armv6k-nintendo-3ds`](platform-support/armv6k-nintendo-3ds.md) | ? |  | Armv6k Nintendo 3DS, Horizon (Requires devkitARM toolchain)
 [`armv7-rtems-eabihf`](platform-support/armv7-rtems-eabihf.md) | ? |  | RTEMS OS for ARM BSPs
 [`armv7-sony-vita-newlibeabihf`](platform-support/armv7-sony-vita-newlibeabihf.md) | ✓ |  | Armv7-A Cortex-A9 Sony PlayStation Vita (requires VITASDK toolchain)
 [`armv7-unknown-linux-uclibceabi`](platform-support/armv7-unknown-linux-uclibceabi.md) | ✓ | ✓ | Armv7-A Linux with uClibc, softfloat
 [`armv7-unknown-linux-uclibceabihf`](platform-support/armv7-unknown-linux-uclibceabihf.md) | ✓ | ? | Armv7-A Linux with uClibc, hardfloat
-`armv7-unknown-freebsd` | ✓ | ✓ | Armv7-A FreeBSD
+[`armv7-unknown-freebsd`](platform-support/freebsd.md) | ✓ | ✓ | Armv7-A FreeBSD
 [`armv7-unknown-netbsd-eabihf`](platform-support/netbsd.md) | ✓ | ✓ | Armv7-A NetBSD w/hard-float
 [`armv7-unknown-trusty`](platform-support/trusty.md) | ? |  |
 [`armv7-wrs-vxworks-eabihf`](platform-support/vxworks.md) | ✓ |  | Armv7-A for VxWorks
@@ -343,9 +343,9 @@ target | std | host | notes
 [`powerpc-unknown-openbsd`](platform-support/powerpc-unknown-openbsd.md) | * |  |
 [`powerpc-wrs-vxworks-spe`](platform-support/vxworks.md) | ✓ |  |
 [`powerpc-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
-`powerpc64-unknown-freebsd` | ✓ | ✓ | PPC64 FreeBSD (ELFv1 and ELFv2)
-`powerpc64le-unknown-freebsd` | ✓ | ✓ | PPC64LE FreeBSD
-`powerpc-unknown-freebsd` | ? |   | PowerPC FreeBSD
+[`powerpc64-unknown-freebsd`](platform-support/freebsd.md) | ✓ | ✓ | PPC64 FreeBSD (ELFv1 and ELFv2)
+[`powerpc64le-unknown-freebsd`](platform-support/freebsd.md) | ✓ | ✓ | PPC64LE FreeBSD
+[`powerpc-unknown-freebsd`](platform-support/freebsd.md) | ? |   | PowerPC FreeBSD
 `powerpc64-unknown-linux-musl` | ? |  | 64-bit PowerPC Linux with musl 1.2.3
 [`powerpc64-wrs-vxworks`](platform-support/vxworks.md) | ✓ |  |
 `powerpc64le-unknown-linux-musl` | ? |  | 64-bit PowerPC Linux with musl 1.2.3, Little Endian

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

@@ -0,0 +1,38 @@
+# \*-unknown-freebsd
+
+**Tier: 2/3**
+
+[FreeBSD] multi-platform 4.4BSD-based UNIX-like operating system.
+
+[FreeBSD]: https://www.FreeBSD.org/
+
+## Target maintainers
+
+- Alan Somers `[email protected]`, https://github.com/asomers
+
+## Requirements
+
+The `x86_64-unknown-freebsd` target is Tier 2 with host tools.
+`i686-unknown-freebsd` is Tier 2 without host tools.  Other targets are Tier 3.
+See [platform-support.md](../platform-support.md) for the full list.
+
+On all architectures, rustc requires FreeBSD version 12 or later to run and
+produces binaries that require FreeBSD version 12, too.  Prior to Rust 1.78.0,
+rustc would run on FreeBSD 10 or later, but build binaries that required
+FreeBSD 11.  libc requires FreeBSD 11 or later.
+
+`extern "C"` uses the official calling convention of the respective architectures.
+
+FreeBSD OS binaries use the ELF file format.
+
+## Building Rust programs
+
+The `x86_64-unknown-freebsd` artifacts are distributed by the rust project and
+may be installed with rustup.  Other targets are built by the ports system and
+may be installed with [pkg(7)](https://man.freebsd.org/cgi/man.cgi?query=pkg)
+or [ports(7)](https://man.freebsd.org/cgi/man.cgi?query=ports).
+
+## Testing
+
+The Rust test suite can be run natively. It can also be run from the ports tree
+with the `make test` command from within the lang/rust directory.