[#1926] workaround for newer openssl on ub18

CMakeLists.txt

@@ -49,6 +49,7 @@ endif()
 set(CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS} -stdlib=libc++ -Wl,-z,defs")
 set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -stdlib=libc++ -Wl,-z,defs")
 add_compile_options(-nostdinc++ -Wall -Wextra -Werror)
+add_compile_options(-Wno-unused-function) # due to OPENSSL_NO_DEPRECATED_1_1_0
 add_compile_options(-Wno-unused-parameter) # Until fix of irods_re_plugin.hpp
 add_compile_options(-Wno-unneeded-internal-declaration) # Until fix of https://github.com/irods/irods/issues/3396
 link_libraries(c++abi curl xml2 crypto pthread)