Fix ngtcp2 Windows cross-build: use ENABLE_LIB_ONLY cmake flag

ngtcp2 CMakeLists.txt doesn't have an ENABLE_EXAMPLES option.
The correct flag to disable building examples is ENABLE_LIB_ONLY,
which is what nixpkgs itself uses for static/FreeBSD builds.

Author: angerman

flake.nix

@@ -109,9 +109,11 @@
            # ngtcp2 examples include POSIX-only headers (sys/socket.h,
            # sys/un.h) that don't exist on Windows. The library itself
            # builds fine; only the example client/server programs fail.
+           # The correct CMake option is ENABLE_LIB_ONLY (not ENABLE_EXAMPLES
+           # which doesn't exist). nixpkgs already sets this for static/FreeBSD.
            ngtcp2 = prev.ngtcp2.overrideAttrs (old: {
              cmakeFlags = (old.cmakeFlags or []) ++ [
-               (prev.lib.cmakeBool "ENABLE_EXAMPLES" false)
+               (prev.lib.cmakeBool "ENABLE_LIB_ONLY" true)
              ];
            });
          });