Add a "fork" of musl as //fusl.

fusl/src/internal/ksigaction.h

Index: fusl/src/internal/ksigaction.h
diff --git a/fusl/src/internal/ksigaction.h b/fusl/src/internal/ksigaction.h
new file mode 100644
index 0000000000000000000000000000000000000000..1d8d9646149b6900e41bf42dcc111e86143369bf
--- /dev/null
+++ b/fusl/src/internal/ksigaction.h
@@ -0,0 +1,11 @@
+/* This is the structure used for the rt_sigaction syscall on most archs,
+ * but it can be overridden by a file with the same name in the top-level
+ * arch dir for a given arch, if necessary. */
+struct k_sigaction {
+	void (*handler)(int);
+	unsigned long flags;
+	void (*restorer)(void);
+	unsigned mask[2];
+};
+
+void __restore(), __restore_rt();