Upstream sets -Werror by default, this is not recommended in Gentoo.

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -325,7 +325,6 @@
         set(YYJSON_BASE_FLAGS
             -pedantic
             -pedantic-errors
-            -Werror
             -Wall
             -Wextra
             -Wconversion