Fix the 'build_all' target for the x64 build.

Currently the x64 build only supports the SyzyAsan RTL unittests but
it'll soon also support building the Clang integration test DLL and
so having a build_all target will make it easier to update what gets
build on the trybots.

Review-Url: https://codereview.chromium.org/2989293002
1 file changed