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

fusl/src/process/posix_spawnattr_sched.c

Index: fusl/src/process/posix_spawnattr_sched.c
diff --git a/fusl/src/process/posix_spawnattr_sched.c b/fusl/src/process/posix_spawnattr_sched.c
new file mode 100644
index 0000000000000000000000000000000000000000..3143635bacc4f43b356affbf2a401e673bc7a1e4
--- /dev/null
+++ b/fusl/src/process/posix_spawnattr_sched.c
@@ -0,0 +1,25 @@
+#include <spawn.h>
+#include <sched.h>
+#include <errno.h>
+
+int posix_spawnattr_getschedparam(const posix_spawnattr_t *restrict attr,
+	struct sched_param *restrict schedparam)
+{
+	return ENOSYS;
+}
+
+int posix_spawnattr_setschedparam(posix_spawnattr_t *restrict attr,
+	const struct sched_param *restrict schedparam)
+{
+	return ENOSYS;
+}
+
+int posix_spawnattr_getschedpolicy(const posix_spawnattr_t *restrict attr, int *restrict policy)
+{
+	return ENOSYS;
+}
+
+int posix_spawnattr_setschedpolicy(posix_spawnattr_t *attr, int policy)
+{
+	return ENOSYS;
+}