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

fusl/src/signal/sigset.c

Index: fusl/src/signal/sigset.c
diff --git a/fusl/src/signal/sigset.c b/fusl/src/signal/sigset.c
new file mode 100644
index 0000000000000000000000000000000000000000..0d7b4564677b8f18d0b10979eb937086cd952007
--- /dev/null
+++ b/fusl/src/signal/sigset.c
@@ -0,0 +1,27 @@
+#include <signal.h>
+
+void (*sigset(int sig, void (*handler)(int)))(int)
+{
+	struct sigaction sa, sa_old;
+	sigset_t mask;
+
+	sigemptyset(&mask);
+	if (sigaddset(&mask, sig) < 0)
+		return SIG_ERR;
+	
+	if (handler == SIG_HOLD) {
+		if (sigaction(sig, 0, &sa_old) < 0)
+			return SIG_ERR;
+		if (sigprocmask(SIG_BLOCK, &mask, &mask) < 0)
+			return SIG_ERR;
+	} else {
+		sa.sa_handler = handler;
+		sa.sa_flags = 0;
+		sigemptyset(&sa.sa_mask);
+		if (sigaction(sig, &sa, &sa_old) < 0)
+			return SIG_ERR;
+		if (sigprocmask(SIG_UNBLOCK, &mask, &mask) < 0)
+			return SIG_ERR;
+	}
+	return sigismember(&mask, sig) ? SIG_HOLD : sa_old.sa_handler;
+}