git-submodule: allow partial update of .git-submodule-status

Allow a specific subdirectory to run git-submodule.sh with only a
subset of submodules, without removing the others from the
.git-submodule-status file.

This also allows scripts/git-submodule.sh to be more lenient:
validating an empty set of submodules is not a mistake.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1 file changed