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/statfs.h

@@ -0,0 +1,7 @@
+struct statfs {
+	unsigned long f_type, f_bsize;
+	fsblkcnt_t f_blocks, f_bfree, f_bavail;
+	fsfilcnt_t f_files, f_ffree;
+	fsid_t f_fsid;
+	unsigned long f_namelen, f_frsize, f_flags, f_spare[4];
+};