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

fusl/src/process/posix_spawnp.c

Index: fusl/src/process/posix_spawnp.c
diff --git a/fusl/src/process/posix_spawnp.c b/fusl/src/process/posix_spawnp.c
new file mode 100644
index 0000000000000000000000000000000000000000..37360001d24bd9ce02ff615a775283a97fb56525
--- /dev/null
+++ b/fusl/src/process/posix_spawnp.c
@@ -0,0 +1,17 @@
+#include <spawn.h>
+#include <unistd.h>
+
+int __execvpe(const char *, char *const *, char *const *);
+
+int __posix_spawnx(pid_t *restrict, const char *restrict,
+	int (*)(const char *, char *const *, char *const *),
+	const posix_spawn_file_actions_t *,
+	const posix_spawnattr_t *restrict, char *const *restrict, char *const *restrict);
+
+int posix_spawnp(pid_t *restrict res, const char *restrict file,
+	const posix_spawn_file_actions_t *fa,
+	const posix_spawnattr_t *restrict attr,
+	char *const argv[restrict], char *const envp[restrict])
+{
+	return __posix_spawnx(res, file, __execvpe, fa, attr, argv, envp);
+}