avoid git.qemu.org (#876)
avoid git.qemu.org (#876)

git.qemu.org seems to be down or under heavy load. Latest qemu
seems to have changed it's .gitmodules to use gitlab.  Since we're
using a github.com mirror, when cloning qemu use rewrite rules to
use github instead of git.qemu.org.  Also install the rewrite rules
recursively into the local config of qemu and it's submodules so
that any further git commands done interactively by the user
will also use github.

Co-authored-by: Tim Snyder <d69a494ecde6fb66a8850ef260a70e1e288b8809@gmail.com>
ucb-bar/chipyard,ucb-bar/chipyard,ucb-bar/chipyard,ucb-bar/chipyard