[build] Move MD_UNWIND_SUPPORT to toplevel libgcc

[Rainer Orth]

Mike Stump <mikestump@comcast.net> writes:

> On Jun 1, 2011, at 9:01 AM, Rainer Orth wrote:
>> Both TARGET_64BIT_DEFAULT and TARGET_BI_ARCH live in gcc only, so at
>> least in the medium term, we need different tests here.
>
> Ah, ick.  Oh well...  The next more general rule would be something like: one can set a feature (implicit -D__GCC_DO_UNWIND_BLA) in the compiler when TARGET_64BIT_DEFAULT and TARGET_BI_ARCH are set a certain way, and then in libgcc, one can just test that feature directly.  Ick, I hate inventing feature names here...

True, but only as a last resort.  Alternatively, one could try to
determine the feature with autoconf.

>> I can certainly do it this way for now, but if we could do away with the
>> tests completely, that would be cleaner.
>
> Agreed, though, I don't believe the test is superfluous.

You still haven't answered my question wrt. Darwin 8 vs. 64-bit on
PowerPC.  Perhaps we can do away with DARWIN_LIBSYSTEM_HAS_UNWIND
completely?

        Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University