Backport @file support from binutils-2.17

@file allows reading command line arguments from a file. Gcc now uses this to
pass very long arguments lists to ld.

ok guenther@ miod@

Merge conflicts, bringing our changes back in:
- extra $(SHELL) and sugar for make (so that files not mode +x still work)
- safer temp file handling
- our W^X binary layout changes in ld
- OpenBSD policy for library file selection in ld
- arm and m88k changes which were not merged in time for official 2.15
- bfd core file handling
- a couple typos

New for 2.15:
- ld(1) and as(1) manpages now generated at build time
- binutils/stabs.c reverted to use our in-tree libiberty for now
- we still use our VIA C3 crypto code over stock binutils, as it recognizes
more instructions
- new emulations for OpenBSD on mips64 machines, to help OpenBSD/sgi
- relaxed %f# handling in gas on OpenBSD/sparc64 (same as was in 2.14)

Tested on all platforms by various people; special thanks to sturm@ and
otto@.

branches: 1.1.1;
Initial revision