Backport configure param --with-git-submodules and set to 'ignore'

Dan Streetmanrequested to merge
ddstreet/qemu:no_git_update into master

As we don't want to update to the latest git submodules since we need a stable reproducable build, and the submodules are included in the deb package source, this prevents updating or validating the git submodules.

This allows having a consistent build with or without a local .git directory.

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