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

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

third_party/git/Documentation/RelNotes/1.7.5.3.txt

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+Git v1.7.5.3 Release Notes
+==========================
+
+Fixes since v1.7.5.2
+--------------------
+
+ * The bash completion scripts should correctly work using zsh's bash
+   completion emulation layer now.
+
+ * Setting $(prefix) in config.mak did not affect where etc/gitconfig
+   file is read from, even though passing it from the command line of
+   $(MAKE) did.
+
+ * The logic to handle "&" (expand to UNIX username) in GECOS field
+   miscounted the length of the name it formatted.
+
+ * "git cherry-pick -s resolve" failed to cherry-pick a root commit.
+
+ * "git diff --word-diff" misbehaved when diff.suppress-blank-empty was
+   in effect.
+
+ * "git log --stdin path" with an input that has additional pathspec
+   used to corrupt memory.
+
+ * "git send-pack" (hence "git push") over smalt-HTTP protocol could
+   deadlock when the client side pack-object died early.
+
+ * Compressed tarball gitweb generates used to be made with the timestamp
+   of the tarball generation; this was bad because snapshot from the same
+   tree should result in a same tarball.
+
+And other minor fixes and documentation updates.