[Bug libstdc++/81507] map header kills variant of vectors

[benni.buch at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81507

--- Comment #1 from Benjamin Buch <benni.buch at gmail dot com> ---
Same with:

$ /home/bebuch/media/programme/gcc-7/bin/g++ --version
g++ (GCC) 7.1.1 20170721
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