rename superh port to "sh" for consistency

linux, gcc, etc. all use "sh" as the name for the superh arch. there
was already some inconsistency internally in musl: the dynamic linker
was searching for "ld-musl-sh.path" as its path file despite its own
name being "ld-musl-superh.so.1". there was some sentiment in both
directions as to how to resolve the inconsistency, but overall "sh"
was favored.

arch/sh/bits/socket.h

@@ -0,0 +1,17 @@
+struct msghdr
+{
+	void *msg_name;
+	socklen_t msg_namelen;
+	struct iovec *msg_iov;
+	int msg_iovlen;
+	void *msg_control;
+	socklen_t msg_controllen;
+	int msg_flags;
+};
+
+struct cmsghdr
+{
+	socklen_t cmsg_len;
+	int cmsg_level;
+	int cmsg_type;
+};