oops another copy of the prototype

crt0 uses a helper function in a MD src/libexec/ld.so .h file (rather than
reproducing the relevant defines and code in a different place) to perform
minor relocations. If things go very wrong, it would call _dl_exit() --
a locally defined crt0 function which is syscall exit(2). We don't need
to call exit(2) for this obscure case which doesn't happen and provides no
debugging information. An 'abort' is going to provide better information.
So let's change the function name to _dso_abort() and make it a single
illegal instruction.
ok guenther

hppa and mips64 have private copies of RCRT0_RELRO(), which should
also perform mimmutable()
ok guenther

Lift the '#ifdef RCRT0' conditional out of boot*.h to crt0.c

Prep for dropping #includes from archdep.h: pull in <machine/reloc.h>
and declare _dl_exit() in boot*.h

ok kettenis@

Split out the hppa and mips64 versions of boot.h similar to how I
split ld.so/boot.c in 2019:
* delete extraneous #includes
* delete jmprel handling on non-hppa
* delete RELOC_GOT() and DT_PROC bits on non-mips64

ok visa@

hppa and mips64 have private copies of RCRT0_RELRO(), which should
also perform mimmutable()
ok guenther

Lift the '#ifdef RCRT0' conditional out of boot*.h to crt0.c

Prep for dropping #includes from archdep.h: pull in <machine/reloc.h>
and declare _dl_exit() in boot*.h

ok kettenis@

Split out the hppa and mips64 versions of boot.h similar to how I
split ld.so/boot.c in 2019:
* delete extraneous #includes
* delete jmprel handling on non-hppa
* delete RELOC_GOT() and DT_PROC bits on non-mips64

ok visa@

Lift the '#ifdef RCRT0' conditional out of boot*.h to crt0.c

Prep for dropping #includes from archdep.h: pull in <machine/reloc.h>
and declare _dl_exit() in boot*.h

ok kettenis@

Split out the hppa and mips64 versions of boot.h similar to how I
split ld.so/boot.c in 2019:
* delete extraneous #includes
* delete jmprel handling on non-hppa
* delete RELOC_GOT() and DT_PROC bits on non-mips64

ok visa@