[tlbuild] mflua c99 trial rebuild

[Mojca Miklavec]

On Tue, 12 Jan 2021 at 22:51, Karl Berry wrote:
>
> If you have a chance, please try to rebuild TL with the current sources
> to see if the mflua addition needs more work in practice. Right now
> we're just hoping that a simple unconditional -std=c99 is enough. That
> won't work for all compilers, but maybe it will work for everything we
> care about?

I suspect that any compiler that can handle C++11 should also be able
to handle C99.
All the platforms that we build on our build farm were OK with the change.

I'm not 100% happy with this solution though.
We already require C99 in tons of other places, but we do it via an
autoconf macro that only adds the flag when necessary. In a way this
flag may force the compiler to downgrade rather than upgrade the
standard (at some point it may become a problem for the newest
compilers, or if some part of the build would require C11/C17 since
the flags cannot be mixed).
But as long as it works ... let it be.

Mojca