wasm: update wasi-libc version

This is necessary for the next commit. It also results in a nice wasm
binary size saving of around 300 bytes.

.github/workflows/windows.yml

@@ -72,7 +72,7 @@ jobs:
         uses: actions/cache@v2
         id: cache-wasi-libc
         with:
-          key: wasi-libc-sysroot-v3
+          key: wasi-libc-sysroot-v4
           path: lib/wasi-libc/sysroot
       - name: Build wasi-libc
         if: steps.cache-wasi-libc.outputs.cache-hit != 'true'