Vagrantfile: Remove system mingw-w64 after installing ours

Just to ensure we don't use the wrong one.

Vagrantfile

@@ -94,6 +94,9 @@ Vagrant.configure(2) do |config|
 
       # the script below will set up the steam-runtime docker containers
       sudo -u vagrant /home/vagrant/proton/vagrant-user-setup.sh
+
+      #ensure we use only the mingw-w64 that we built
+      apt-get remove -y '*mingw-w64*'
     SHELL
   end
 end

build-mingw-w64.sh

@@ -5,6 +5,8 @@ set -e
 if [ -z "$1" ]; then
     echo "Makes a local build of mingw-w64 in this directory and installs it to the given path."
     echo ""
+    echo "Note: Requires a system mingw-w64 to be present already, for us to bootstrap with."
+    echo ""
     echo "usage:"
     echo -e "\t$0 <installation path e.g. \$HOME/.local>"
     exit 1