Make 'USE_BUNDLED_ZLIB' configurable

Signed-off-by: Paulo Gomes <paulo.gomes@weave.works>

Author: Paulo Gomes

hack/Makefile

@@ -127,7 +127,7 @@ $(LIBGIT2):
 		-DBUILD_CLAR:BOOL:BOOL=OFF \
 		-DTHREADSAFE:BOOL=ON \
 		-DBUILD_SHARED_LIBS:BOOL=$(BUILD_SHARED_LIBS) \
-		-DUSE_BUNDLED_ZLIB:BOOL=OFF \
+		-DUSE_BUNDLED_ZLIB:BOOL=$(USE_BUNDLED_ZLIB) \
 		-DUSE_HTTP_PARSER:STRING=builtin  \
 		-DREGEX_BACKEND:STRING=builtin \
 		-DUSE_HTTPS:STRING=$(USE_HTTPS) \