help: print zlib-ng version number

When building against zlib-ng, the header file `zlib.h` is not included,
but `zlib-ng.h` is included instead. It's `zlib.h` that defines
`ZLIB_VERSION` and that macro is used to print out zlib version in
`git-version(1)` with `--build-options`. But when it's not defined, no
version is printed.

`zlib-ng.h` defines another macro: `ZLIBNG_VERSION`. Use that macro to
print the zlib-ng version in `git version --build-options` when it's
set. Otherwise fallback to `ZLIB_VERSION`.

Signed-off-by: Toon Claes <toon@iotcl.com>
Helped-by: Patrick Steinhardt <ps@pks.im>
Reviewed-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: To1ne

help.c

@@ -776,7 +776,9 @@ void get_version_info(struct strbuf *buf, int show_build_options)
 #if defined OPENSSL_VERSION_TEXT
 		strbuf_addf(buf, "OpenSSL: %s\n", OPENSSL_VERSION_TEXT);
 #endif
-#if defined ZLIB_VERSION
+#if defined ZLIBNG_VERSION
+		strbuf_addf(buf, "zlib-ng: %s\n", ZLIBNG_VERSION);
+#elif defined ZLIB_VERSION
 		strbuf_addf(buf, "zlib: %s\n", ZLIB_VERSION);
 #endif
 	}

t/t0091-bugreport.sh

@@ -47,7 +47,8 @@ test_expect_success 'sanity check "System Info" section' '
 	# This is bound to differ from environment to environment,
 	# so we just do some rather high-level checks.
 	grep "uname: ." system &&
-	grep "compiler info: ." system
+	grep "compiler info: ." system &&
+	grep "zlib." system
 '
 
 test_expect_success 'dies if file with same name as report already exists' '