[patch] Clean up detection of SJLJ exceptions in target libraries

[Eric Botcazou]

> This patch fixes an issue preventing mingw-w64 i686 dwarf2-eh
> bootstrapping described at:
> 
> http://sourceforge.net/p/mingw-w64/mailman/message/34101954/
> 
> I'm assuming this has more to do with switching away from the current
> sjlj configuration method since configuring gcc with
> "--disable-sjlj-exceptions --with-dwarf2" still suffers the same
> issues.  Building with simply "--with-dwarf2" instead, however, now
> works fine.  I'm not sure whether or not a bug has been created for it
> and if one needs to be.

Yes, if it makes any difference for a --with-dwarf2 bootstrap, this means that 
gcc and libgcc had different views of the EH scheme of the compiler.

The --disable-sjlj-exceptions breakage is worth investigating separately, so 
please create a PR with Bugzilla (https://gcc.gnu.org/bugzilla) for it.

-- 
Eric Botcazou