github: Disable zstd in the macos github actions build

Zstd is available and gets autodetected, but it's only available in
native form, not in arm64 form.

Also, for the existing workaround, instead of entirely disabling lldb,
one could pass -DLLDB_ENABLE_PYTHON=OFF instead.

.github/workflows/build.yml

@@ -94,7 +94,9 @@ jobs:
           # Building with MACOS_REDIST=1 (building universal binaries) without
           # --disable-lldb fails in Github Actions, because python is available
           # (and gets picked up), but only exists in native form.
-          MACOS_REDIST=1 ./build-all.sh $(pwd)/install/llvm-mingw --disable-clang-tools-extra --disable-lldb
+          # Disable use of zstd too - it's also available, but only in native
+          # form.
+          MACOS_REDIST=1 LLVM_CMAKEFLAGS="-DLLVM_ENABLE_ZSTD=OFF" ./build-all.sh $(pwd)/install/llvm-mingw --disable-clang-tools-extra --disable-lldb
           cd install
           tar -Jcf ../llvm-mingw-macos.tar.xz llvm-mingw
       - uses: actions/upload-artifact@v2