Don't use -Werror=deprecated.
--- CMakeLists.txt.orig	2020-07-12 14:33:44.000000000 -0500
+++ CMakeLists.txt	2020-09-05 05:26:37.000000000 -0500
@@ -248,7 +248,6 @@
   wl_add_flag(WL_COMPILE_DIAGNOSTICS "-Wno-unreachable-code")
   wl_add_flag(WL_COMPILE_DIAGNOSTICS "-Wno-documentation")
 
-  wl_add_flag(WL_COMPILE_DIAGNOSTICS "-Werror=deprecated")
   wl_add_flag(WL_COMPILE_DIAGNOSTICS "-Werror=non-pod-varargs")
 
   wl_add_flag(WL_COMPILE_DIAGNOSTICS "-Qunused-arguments")