maint: sync latest bootstrap from gnulib

* bootstrap: Should have updated this with the last gnulib update.

bootstrap

@@ -1,6 +1,6 @@
 #! /bin/sh
 # Print a version string.
-scriptversion=2021-04-11.09; # UTC
+scriptversion=2022-03-21.01; # UTC
 
 # Bootstrap this package from checked-out sources.
 
@@ -763,9 +763,26 @@ if $use_gnulib; then
       shallow=
       if test -z "$GNULIB_REVISION"; then
         git clone -h 2>&1 | grep -- --depth > /dev/null && shallow='--depth 2'
+        git clone $shallow ${GNULIB_URL:-$default_gnulib_url} "$gnulib_path" \
+          || cleanup_gnulib
+      else
+        git fetch -h 2>&1 | grep -- --depth > /dev/null && shallow='--depth 2'
+        mkdir -p "$gnulib_path"
+        # Only want a shallow checkout of $GNULIB_REVISION, but git does not
+        # support cloning by commit hash. So attempt a shallow fetch by commit
+        # hash to minimize the amount of data downloaded and changes needed to
+        # be processed, which can drastically reduce download and processing
+        # time for checkout. If the fetch by commit fails, a shallow fetch can
+        # not be performed because we do not know what the depth of the commit
+        # is without fetching all commits. So fallback to fetching all commits.
+        git -C "$gnulib_path" init
+        git -C "$gnulib_path" remote add origin \
+            ${GNULIB_URL:-$default_gnulib_url}
+        git -C "$gnulib_path" fetch $shallow origin "$GNULIB_REVISION" \
+          || git -C "$gnulib_path" fetch origin \
+          || cleanup_gnulib
+        git -C "$gnulib_path" reset --hard FETCH_HEAD
       fi
-      git clone $shallow ${GNULIB_URL:-$default_gnulib_url} "$gnulib_path" \
-        || cleanup_gnulib
 
       trap - 1 2 13 15
     fi
@@ -1093,7 +1110,7 @@ bootstrap_epilogue
 
 echo "$0: done.  Now you can run './configure'."
 
-# Local variables:
+# Local Variables:
 # eval: (add-hook 'before-save-hook 'time-stamp)
 # time-stamp-start: "scriptversion="
 # time-stamp-format: "%:y-%02m-%02d.%02H"