version: teach --build-options to reports zlib version information

Show ZLIB_VERSION, if defined, in "git version --build-options"
output.

Signed-off-by: Randall S. Becker <rsbecker@nexbridge.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

help.c

@@ -766,6 +766,9 @@ void get_version_info(struct strbuf *buf, int show_build_options)
 #endif
 #if defined OPENSSL_VERSION_TEXT
 		strbuf_addf(buf, "OpenSSL: %s\n", OPENSSL_VERSION_TEXT);
+#endif
+#if defined ZLIB_VERSION
+		strbuf_addf(buf, "zlib: %s\n", ZLIB_VERSION);
 #endif
 	}
 }