Bug 1450088 - Build clang with libxml2 support. r=froydnj

This is required for llvm-mt, which building winchecksec will require.
We do a dummy change to build-clang.sh so as to change the toolchain
index hash.

Differential Revision: https://phabricator.services.mozilla.com/D68153

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

build/build-clang/build-clang.py

@@ -276,6 +276,7 @@ def build_one_stage(cc, cxx, asm, ld, ar, ranlib, libtool,
             cmake_args += ["-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=WebAssembly"]
         if is_linux():
             cmake_args += ["-DLLVM_BINUTILS_INCDIR=%s/include" % gcc_dir]
+            cmake_args += ["-DLLVM_ENABLE_LIBXML2=FORCE_ON"]
         if is_windows():
             cmake_args.insert(-1, "-DLLVM_EXPORT_SYMBOLS_FOR_PLUGINS=ON")
             cmake_args.insert(-1, "-DLLVM_USE_CRT_RELEASE=MT")

taskcluster/docker/mingw32-build/Dockerfile

@@ -26,6 +26,7 @@ RUN apt-get update && \
       gnupg \
       jq \
       libucl1 \
+      libxml2 \
       patch \
       p7zip-full \
       scons \

taskcluster/docker/toolchain-build/Dockerfile

@@ -29,6 +29,7 @@ RUN apt-get update && \
       libbz2-dev \
       libcurl4-openssl-dev \
       libssl-dev \
+      libxml2-dev \
       libtool \
       libucl-dev \
       ninja-build \