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

fusl/src/exit/assert.c

Index: fusl/src/exit/assert.c
diff --git a/fusl/src/exit/assert.c b/fusl/src/exit/assert.c
new file mode 100644
index 0000000000000000000000000000000000000000..e87442a7c50d9ca8fdf267d7c6038780941c56d3
--- /dev/null
+++ b/fusl/src/exit/assert.c
@@ -0,0 +1,9 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+void __assert_fail(const char *expr, const char *file, int line, const char *func)
+{
+	fprintf(stderr, "Assertion failed: %s (%s: %s: %d)\n", expr, file, func, line);
+	fflush(NULL);
+	abort();
+}