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

fusl/arch/mips/ksigaction.h

+struct k_sigaction {
+        unsigned flags;
+        void (*handler)(int);
+        unsigned long mask[4];
+        /* The following field is past the end of the structure the
+         * kernel will read or write, and exists only to avoid having
+         * mips-specific preprocessor conditionals in sigaction.c. */
+        void (*restorer)();
+};
+
+void __restore(), __restore_rt();