platform-support.md: It's now verified that NetBSD/riscv64 can self-host.

Author: he32

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

@@ -305,7 +305,7 @@ target | std | host | notes
 `riscv64gc-unknown-freebsd` |   |   | RISC-V FreeBSD
 `riscv64gc-unknown-fuchsia` |   |   | RISC-V Fuchsia
 `riscv64gc-unknown-linux-musl` |   |   | RISC-V Linux (kernel 4.20, musl 1.2.0)
-[`riscv64gc-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ? | RISC-V NetBSD
+[`riscv64gc-unknown-netbsd`](platform-support/netbsd.md) | ✓ | ✓ | RISC-V NetBSD
 [`riscv64gc-unknown-openbsd`](platform-support/openbsd.md) | ✓ | ✓ | OpenBSD/riscv64
 `s390x-unknown-linux-musl` |  |  | S390x Linux (kernel 3.2, MUSL)
 `sparc-unknown-linux-gnu` | ✓ |  | 32-bit SPARC Linux