maint: bootstrap: sync submodule usage from gnulib

* bootstrap: Config for git submodule use only if .gitmodules exists.

diff --git a/bootstrap b/bootstrap
index 2731b7e..8fb2f2c 100755 (executable)
--- a/bootstrap
+++ b/bootstrap
@@ -342,7 +342,7 @@ cleanup_gnulib() {
 }
 
 git_modules_config () {
-  GIT_CONFIG=.gitmodules git config "$@"
+  test -f .gitmodules && git config --file .gitmodules "$@"
 }
 
 # Get gnulib files.