merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/t/perf/p5600-clone-reference.sh

@@ -0,0 +1,27 @@
+#!/bin/sh
+
+test_description='speed of clone --reference'
+. ./perf-lib.sh
+
+test_perf_default_repo
+
+test_expect_success 'create shareable repository' '
+	git clone --bare . shared.git
+'
+
+test_expect_success 'advance base repository' '
+	# Do not use test_commit here; its test_tick will
+	# use some ancient hard-coded date. The resulting clock
+	# skew will cause pack-objects to traverse in a very
+	# sub-optimal order, skewing the results.
+	echo content >new-file-that-does-not-exist &&
+	git add new-file-that-does-not-exist &&
+	git commit -m "new commit"
+'
+
+test_perf 'clone --reference' '
+	rm -rf dst.git &&
+	git clone --no-local --bare --reference shared.git . dst.git
+'
+
+test_done