previously it was using the same name as the default ABI with hard
float (floating point args and return value in registers).

the test __SH_FPU_ANY__ || __SH4__ matches what's used in the
configure script already, and seems correct under casual review
against gcc's config/sh.h, but may need tweaks. the logic for
predefined macros for sh, and what they all mean, is very complex.
eventually this should be documented in comments here.

configure already rejects "half-hard" configurations on sh where
double=float since these do not conform to Annex F and are not
suitable for musl, so these do not need to be considered here.

versions of reloc.h that rely on endian macros much include endian.h
to ensure they are available.

this overhaul further reduces the amount of arch-specific code needed
by the dynamic linker and removes a number of assumptions, including:

- that symbolic function references inside libc are bound at link time
  via the linker option -Bsymbolic-functions.

- that libc functions used by the dynamic linker do not require
  access to data symbols.

- that static/internal function calls and data accesses can be made
  without performing any relocations, or that arch-specific startup
  code handled any such relocations needed.

removing these assumptions paves the way for allowing libc.so itself
to be built with stack protector (among other things), and is achieved
by a three-stage bootstrap process:

1. relative relocations are processed with a flat function.
2. symbolic relocations are processed with no external calls/data.
3. main program and dependency libs are processed with a
   fully-functional libc/ldso.

reduction in arch-specific code is achived through the following:

- crt_arch.h, used for generating crt1.o, now provides the entry point
  for the dynamic linker too.

- asm is no longer responsible for skipping the beginning of argv[]
  when ldso is invoked as a command.

- the functionality previously provided by __reloc_self for heavily
  GOT-dependent RISC archs is now the arch-agnostic stage-1.

- arch-specific relocation type codes are mapped directly as macros
  rather than via an inline translation function/switch statement.

this was one of the main instances of ugly code duplication: all archs
use basically the same types of relocations, but roughly equivalent
logic was duplicated for each arch to account for the different naming
and numbering of relocation types and variation in whether REL or RELA
records are used.

as an added bonus, both REL and RELA are now supported on all archs,
regardless of which is used by the standard toolchain.

the following issues are fixed:

- R_SH_REL32 was adding the load address of the module being relocated
  to the result. this seems to have been a mistake in the original
  port, since it does not match other dynamic linker implementations
  and since adding a difference between two addresses (the symbol
  value and the relocation address) to a load address does not make
  sense.

- R_SH_TLS_DTPMOD32 was wrongly accepting an inline addend (i.e. using
  += rather than = on *reloc_addr) which makes no sense; addition is
  not an operation that's defined on module ids.

- R_SH_TLS_DTPOFF32 and R_SH_TLS_TPOFF32 were wrongly using inline
  addends rather than the RELA-provided addends.

in addition, handling of R_SH_GLOB_DAT, R_SH_JMP_SLOT, and R_SH_DIR32
are merged to all honor the addend. the first two should not need it
for correct usage generated by toolchains, but other dynamic linkers
allow addends here, and it simplifies the code anyway.

these issues were spotted while reviewing the code for the purpose of
refactoring this part of the dynamic linker. no testing was performed.

the immediate motivation is supporting TLSDESC relocations which
require allocation and thus may fail (unless we pre-allocate), but
this mechanism should also be used for throwing an error on
unsupported or invalid relocation types, and perhaps in certain cases,
for reporting when a relocation is not satisfiable.

default endianness for sh on linux is little, and while conventions
vary, "eb" seems to be the most widely used suffix for big endian.

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.