Support dead-stripping in ELF objects

[Robinson, Paul]

Okay, after a vacation and tracking down a bug in this stuff reported
by an internal user, I'll have another go at this.

The previous discussion resulted in a proposal to define 3 new ELF
section-header flags and one symbol flag.  However this forum does not
have the authority to muck with the definition of ELF, so I'm not
going to implement that.  I have added FIXME comments to indicate
where you *would* set those section-header flags.  Anyone so inclined
to go through whatever the process would be to get new flags defined
for ELF section headers, do so with my blessing.

(My target sets an ELF file-header flag, that field is already
target-specific so we have no qualms about doing it that way.  Our
linker a-priori knows which sections to consider for dead-stripping.)

Attaching the revised patch.
--paulr

-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: Deadstrip2-diff.txt
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20130503/86e98855/attachment.txt>