https://bugzilla.mozilla.org/show_bug.cgi?id=1874059
https://github.com/llvm/llvm-project/issues/79027
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=276746

Index: build/moz.configure/toolchain.configure
--- build/moz.configure/toolchain.configure.orig
+++ build/moz.configure/toolchain.configure
@@ -2290,7 +2290,7 @@ set_define("_LIBCPP_HIDE_FROM_ABI", libcxx_override_vi
 @depends(target, build_environment)
 def visibility_flags(target, env):
     if target.os != "WINNT":
-        if target.kernel == "Darwin":
+        if target.kernel == "Darwin" or target.kernel == "OpenBSD":
             return ("-fvisibility=hidden", "-fvisibility-inlines-hidden")
         return (
             "-I%s/system_wrappers" % os.path.join(env.dist),
