[Bug libstdc++/85824] regex constructor crashes under UTF-8 locale on Solaris SPARC when parsing a simple character class

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85824

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We should also consider only caching chars in the range 0-127, because
otherwise as this bug shows we call transform_primary for 128 char values which
always fail.