[tlbuild] trial builds for TL'13

[Karl Berry]

    kpathsea/c-memstr.h loads <string.h> while FileFinder.cpp loads
    <string> which caused the problem.

Thanks, but that patch looks too intrusive to me.  I doubt we want
to omit reading <string.h> in every compilation using g++ just because
one file in dvisvgm creates a conflict.  There has to be a better way to
handle it.  Preferably by changing dvisvgm, not kpathsea.

The other patch, for uposixdefs.h, also looks problematic to me, I'm
sorry to say.  It would affect not just your compilations with the
latest OpenSolaris but any compilation on a Sun with any version of any
OS.  It does not seem implausible to me that _XOPEN_SOURCE_EXTENDED is
actually desirable/needed in other cases ...

Best,
Karl