We need to include <cstring> because memset() is defined there.
    oi-userland/components/shell/fish/fish-3.6.0/src/fds.cpp:204:5: error: 'memset' was not declared in this scope
      204 |     FD_ZERO(&fds);

--- fish-3.6.0/src/fds.cpp.orig	2023-01-07 15:12:25.000000000 +0000
+++ fish-3.6.0/src/fds.cpp	2023-01-08 10:55:33.610119460 +0000
@@ -17,6 +17,9 @@
 #include <sys/eventfd.h>
 #endif
 
+// memset() is defined in cstring:
+#include <cstring>
+
 // The first fd in the "high range." fds below this are allowed to be used directly by users in
 // redirections, e.g. >&3
 const int k_first_high_fd = 10;