Add elf64-sparc TLS support.

[Eric Botcazou]

> A testcase that emits the .vtable_* assembler?  Sure,
> simply build src/ld/testsuite/ld-selective/3.cc
>
> Oh I see, it was using gcc-3.3.x for those tests in my
> build.
>
> gcc-3.3.x emits the .vtable_* stuff, gcc-3.4 does not.

OK, it's the -fvtable-gc option, which was removed in 3.4 but indeed still 
emits the .vtable stuff as of 3.3.  Not sure whether we should "enhance" the 
SPARC64 linker though.

I asked for more details because I had never seen .vtable in any SPARC 
assembly code.  Obviously I didn't know of -fvtable-gc.

-- 
Eric Botcazou