Patch from Stefan Allius and Edie C. Dost to add SuperH

Patch from Stefan Allius and Edie C. Dost to add SuperH
shared library support.  This also adds some cleaner error
handling, which I (Erik) then ported over to x86 and arm.
In addition Stefan added the following fixes:

- in hash.c was the lvalue handling of global library functions wrong.
   To fix this I had to change the prototype of _dl_find_hash. (==> TIS and
   ELF spec. Vers. 1.2)

- in ldso.c was the order of the .init sections calls wrong. Before we call
  the initialization code of a library we have to check that all dependend
  libraries are already initialized. This can easily made by calling it in the
  revers loading order. For this I added a previous pointer chain.

- in ldso.c the ELF magics wasn't checked fo PPC, MIPS and SH architecture