ntlmclient: silence deprecation warnings for CommonCrypto backend

The `CC_MD4()` function has been deprecated in macOS 10.15. Silence this
warning for now until we implement a proper fix.

deps/ntlmclient/CMakeLists.txt

@@ -7,6 +7,8 @@ DISABLE_WARNINGS(implicit-fallthrough)
 IF (HTTPS_BACKEND STREQUAL "SecureTransport")
 	ADD_DEFINITIONS(-DCRYPT_COMMONCRYPTO)
 	SET(SRC_NTLMCLIENT_CRYPTO "crypt_commoncrypto.c")
+	# CC_MD4 has been deprecated in macOS 10.15.
+	SET_SOURCE_FILES_PROPERTIES("crypt_commoncrypto.c" COMPILE_FLAGS "-Wno-deprecated")
 ELSEIF (HTTPS_BACKEND STREQUAL "OpenSSL")
 	ADD_DEFINITIONS(-DCRYPT_OPENSSL)
 	INCLUDE_DIRECTORIES(${OPENSSL_INCLUDE_DIR})