[tlbuild] dvisvgm-2.1 trial build

[Karl Berry]

    kb>
    -AX_CXX_COMPILE_STDCXX([11], [noext])
    +AX_CXX_COMPILE_STDCXX([11])

Ken, I sent the idea to Martin. Will see what he says.

    dk> Maybe this information could be used to fix then TeXLive source 

Dick, I sent this info to Martin also. Better to make changes upstream
than in TL, if at all possible, after all.

We'll see ... thanks, karl.