Fix mistake in x86_64-unknown-freebsd platform description

Author: ehuss

Diff for: src/doc/rustc/src/platform-support.md

@@ -101,7 +101,7 @@ 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`](platform-support/freebsd.md) | 64-bit amd64 FreeBSD
+[`x86_64-unknown-freebsd`](platform-support/freebsd.md) | 64-bit x86 FreeBSD
 [`x86_64-unknown-illumos`](platform-support/illumos.md) | illumos
 `x86_64-unknown-linux-musl` | 64-bit Linux with musl 1.2.3
 [`x86_64-unknown-netbsd`](platform-support/netbsd.md) | NetBSD/amd64