On some platforms, you'll want to support READ_IMPLIES_EXEC differently
depending on personality (e.g, native binary vs. x86 binary).

This supports that (and makes the code more readable while at it) by
replacing the old architecture-specific fixed LEGACY_BINARIES macro
define with a architecture-specific "elf_read_implies_exec_binary()"
helper function.

For now, x86 is the only user, and sets the "read implies exec" bit for
legacy apps.  ia64 and x86-64 are likely to want to do their own thing.

Acked by Ingo.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>