Rollup merge of #123421 - taiki-e:netbsd-doc, r=Nilstrieb

Fix target name in NetBSD platform-support doc

NetBSD platform-support doc currently mentions `amd64-unknown-netbsd`, but it is not a valid target name (the correct name is `x86_64-unknown-netbsd`).

https://github.com/rust-lang/rust/blob/ceab6128fa48a616bfd3e3adf4bc80133b8ee223/src/doc/rustc/src/platform-support/netbsd.md?plain=1#L16

```console
$ rustc --print target-list | grep netbsd
aarch64-unknown-netbsd
aarch64_be-unknown-netbsd
armv6-unknown-netbsd-eabihf
armv7-unknown-netbsd-eabihf
i586-unknown-netbsd
i686-unknown-netbsd
mipsel-unknown-netbsd
powerpc-unknown-netbsd
riscv64gc-unknown-netbsd
sparc64-unknown-netbsd
x86_64-unknown-netbsd
```

Author: matthiaskrgr