Update with status for various NetBSD ports.

The NetBSD ports of rust to aarch64, armv7*, i686, and powerpc**
all both build and run.

*) Natively requires repeated successive build attempts (rustc is
   such a resource pig VM-consumption-wise), or run in a chroot
   on an aarch64 host where the available VM space is 4GB instead
   of the native 2GB.
**) Powerpc either requires -latomic in a directory searched by
   default by 'ld' or to be built within pkgsrc which has a patch
   to tackle this.

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

@@ -156,7 +156,7 @@ target | std | host | notes
 `aarch64-apple-tvos` | * |  | ARM64 tvOS
 `aarch64-unknown-freebsd` | ✓ | ✓ | ARM64 FreeBSD
 `aarch64-unknown-hermit` | ? |  |
-`aarch64-unknown-netbsd` | ? |  |
+`aarch64-unknown-netbsd` | ✓ | ✓ |
 `aarch64-unknown-openbsd` | ✓ | ✓ | ARM64 OpenBSD
 `aarch64-unknown-redox` | ? |  | ARM64 Redox OS
 `aarch64-uwp-windows-msvc` | ? |  |
@@ -166,7 +166,7 @@ target | std | host | notes
 `armv6-unknown-netbsd-eabihf` | ? |  |
 `armv7-apple-ios` | ✓ |  | ARMv7 iOS, Cortex-a8
 `armv7-unknown-freebsd` | ✓ | ✓ | ARMv7 FreeBSD
-`armv7-unknown-netbsd-eabihf` | ? |  |
+`armv7-unknown-netbsd-eabihf` | ✓ | ✓ |
 `armv7-wrs-vxworks-eabihf` | ? |  |
 `armv7a-none-eabihf` | * | | ARM Cortex-A, hardfloat
 `armv7s-apple-ios` | ✓ |  |
@@ -177,7 +177,7 @@ target | std | host | notes
 `i686-pc-windows-msvc` | ✓ |  | 32-bit Windows XP support
 `i686-unknown-uefi` | ? |  | 32-bit UEFI
 `i686-unknown-haiku` | ✓ | ✓ | 32-bit Haiku
-`i686-unknown-netbsd` | ✓ |  | NetBSD/i386 with SSE2
+`i686-unknown-netbsd` | ✓ | ✓ | NetBSD/i386 with SSE2
 `i686-unknown-openbsd` | ✓ | ✓ | 32-bit OpenBSD
 `i686-uwp-windows-gnu` | ? |  |
 `i686-uwp-windows-msvc` | ? |  |
@@ -193,7 +193,7 @@ target | std | host | notes
 `msp430-none-elf` | * |  | 16-bit MSP430 microcontrollers
 `powerpc-unknown-linux-gnuspe` | ✓ |  | PowerPC SPE Linux
 `powerpc-unknown-linux-musl` | ? |  |
-`powerpc-unknown-netbsd` | ? |  |
+`powerpc-unknown-netbsd` | ✓ | ✓ |
 `powerpc-wrs-vxworks` | ? |  |
 `powerpc-wrs-vxworks-spe` | ? |  |
 `powerpc64-unknown-freebsd` | ✓ | ✓ | PPC64 FreeBSD (ELFv1 and ELFv2)