[tlbuild] gcc-10 changes behavior, and a simple workaround

[Nelson H. F. Beebe]

The bleeding-edge Fedora 32 Rawhide distribution of GNU/Linux advances
the gcc compiler major version to 10, and there is a behavior change
in the new compilers that breaks TeX Live 2020 builds.

The problem, and its repair, is documented here:

	http://www.math.utah.edu/pub/texlive-utah-2020/README.html#fedora-32

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- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
- University of Utah                    FAX: +1 801 581 4148                  -
- Department of Mathematics, 110 LCB    Internet e-mail: beebe at math.utah.edu  -
- 155 S 1400 E RM 233                       beebe at acm.org  beebe at computer.org -
- Salt Lake City, UT 84112-0090, USA    URL: http://www.math.utah.edu/~beebe/ -
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