[patch i386 mingw]: Disallow DW2 unwind for 64-bit and multilib

[Kai Tietz <Kai dot Tietz at onevision dot com>]

Hello,

this patch disables the use of DW2 unwind (DWARF2_UNWIND_INFO) for 64-bit 
and multilib builds. It stops build of gcc by an error message for 
multilib x86, when sjlj isn't the default unwind mechanism. This is 
necessary, as 64-bit Windows DW2 unwind isn't supported and a switching 
between those both mechanisms in multilib isn't possible.

ChangeLog

2009-07-24  Kai Tietz  <kai.tietz@onevision.com>

        * config/i386/cygming.h (DWARF2_UNWIND_INFO): Error build when
        TARGET_BI_ARCH is specified without SJLJ.
        * config/i386/mingw32.h (MD_UNWIND_SUPPORT): Define it, 
if!TARGET_64BIT
        and TARGET_BI_ARCH aren't defined.

Tested for i686-pc-mingw32 and x86_64-w64-mingw32.
I will apply this patch in some hours if there are no objections.

Cheers,
Kai



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