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/crt_arch.h

@@ -0,0 +1,9 @@
+__asm__("\
+.global _start \n\
+_start: \n\
+	mov r15, r4 \n\
+	mov #-16, r0 \n\
+	and r0, r15 \n\
+	bsr __cstart \n\
+	nop \n\
+");