Bug 1596219 - Augment wasi sysroot from bug 1582192 with bits necessary to perform wasm builds r=froydnj

Build a full sysroot by downloading the `wasi-sdk` repo, which has `llvm-project` and `wasi-libc` as submodules. `wasi-sdk` builds a `clang` in a unique configuration (with `wasm32-wasi` as a default target) and uses that `clang` to build the rest of the pieces for the wasm sysroot.

In principle it should be possible to build the sysroot using our in-house automation-built `clang`, but I kept running into strange, hard-to-diagnose issues when I attempted that. If someone else is able to straighten out all the compilation issues, we could replace this script and stop pulling in `wasi-sdk` entirely, which would result in a build that takes much less time overall. Until then, this will have to do to unblock the rest of the wasm sandboxing work.

Differential Revision: https://phabricator.services.mozilla.com/D54560

--HG--
extra : moz-landing-system : lando

taskcluster/ci/fetch/toolchains.yml

@@ -415,12 +415,12 @@ clang-9:
         repo: https://github.com/llvm/llvm-project
         revision: 0399d5a9682b3cef71c653373e38890c63c4c365
 
-wasi-libc:
-    description: wasi-libc source code
+wasi-sdk:
+    description: wasi-sdk source code
     fetch:
         type: git
-        repo: https://github.com/CraneStation/wasi-libc
-        revision: c35f0f5dd64ad982bbad71f3e3a8942a1029c1e6
+        repo: https://github.com/CraneStation/wasi-sdk
+        revision: 5225b05436ce57f01fe649f411f3ff701246628b
 
 ninja:
     description: ninja 1.9.0

taskcluster/ci/toolchain/misc.yml

@@ -168,9 +168,10 @@ wasi-sysroot:
         toolchain-artifact: public/build/wasi-sysroot.tar.xz
     fetches:
         fetch:
-            - wasi-libc
+            - wasi-sdk
         toolchain:
-            - linux64-clang
+            - linux64-binutils
+            - linux64-gcc-7
 
 wrench-deps:
     description: "Downloads all the crates needed for building wrench"

taskcluster/scripts/misc/build-wasi-sysroot.sh

@@ -1,18 +1,11 @@
 #!/bin/bash
 set -x -e -v
 
-# This script is for building libc-wasi.
-
-cd $GECKO_PATH
-
-# gets a bit too verbose here
-
-cd $MOZ_FETCHES_DIR/wasi-libc
-make WASM_CC=$MOZ_FETCHES_DIR/clang/bin/clang \
-     WASM_AR=$MOZ_FETCHES_DIR/clang/bin/llvm-ar \
-     WASM_NM=$MOZ_FETCHES_DIR/clang/bin/llvm-nm \
-     SYSROOT=$(pwd)/wasi-sysroot
-
+export PATH="$MOZ_FETCHES_DIR/gcc/bin:$MOZ_FETCHES_DIR/binutils/bin:$PATH"
+export LD_LIBRARY_PATH="$MOZ_FETCHES_DIR/gcc/lib64/:$LD_LIBRARY_PATH"
+cd $MOZ_FETCHES_DIR/wasi-sdk
+PREFIX=$MOZ_FETCHES_DIR/wasi-sdk/wasi-sysroot
+make PREFIX=$PREFIX
 # Put a tarball in the artifacts dir
 mkdir -p $UPLOAD_DIR
-tar caf $UPLOAD_DIR/wasi-sysroot.tar.xz wasi-sysroot
+tar -C $MOZ_FETCHES_DIR/wasi-sdk/ -caf $UPLOAD_DIR/wasi-sysroot.tar.xz wasi-sysroot