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.
fix endian subarchs for sh arch

default endianness for sh on linux is little, and while conventions
vary, "eb" seems to be the most widely used suffix for big endian.
add nofpu subarchs to the sh arch, and properly detect compiler's fpu config
fix copy-and-paste error in configure's IEEE double check for sh
fix missing CFLAGS in configure test for float on sh
improve configure's target arch matching

most notably, it was failing to match sh4-*, etc., but in general the
explicit matching of hyphens for some archs was problematic because it
failed to accept simply the musl-style arch name (without a gcc-style
tuple) as an input. the original motivation of matching hyphens was to
prevent incorrectly identifying a 64-bit arch as the corresponding
32-bit arch (e.g. mips* matching mips64) but this is easily fixed by
simply checking (and for now, rejecting as unsupported) the relevant
64-bit archs.