Rollup merge of rust-lang#70159 - alexcrichton:update-wasi, r=pietroalbini

Update the bundled wasi-libc with libstd

Brings in WebAssembly/wasi-libc#184 which can help standalone programs
with environment variables!

Author: Centril

src/ci/docker/dist-various-2/build-wasi-toolchain.sh

@@ -12,7 +12,7 @@ export PATH=`pwd`/clang+llvm-9.0.0-x86_64-linux-gnu-ubuntu-14.04/bin:$PATH
 git clone https://github.com/CraneStation/wasi-libc
 
 cd wasi-libc
-git reset --hard 1fad33890a5e299027ce0eab7b6ad5260585e347
+git reset --hard 9efc2f428358564fe64c374d762d0bfce1d92507
 make -j$(nproc) INSTALL_DIR=/wasm32-wasi install
 
 cd ..