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/fenv.h

@@ -0,0 +1,17 @@
+#define FE_TONEAREST  0
+#define FE_TOWARDZERO 1
+
+#define FE_INEXACT    0x04
+#define FE_UNDERFLOW  0x08
+#define FE_OVERFLOW   0x10
+#define FE_DIVBYZERO  0x20
+#define FE_INVALID    0x40
+#define FE_ALL_EXCEPT 0x7c
+
+typedef unsigned long fexcept_t;
+
+typedef struct {
+	unsigned long __cw;
+} fenv_t;
+
+#define FE_DFL_ENV    ((const fenv_t *) -1)