Master uncompilable on cygwin

[Enrico Forestieri]

This is the error:

In file included from ../../../../src/frontends/qt/GuiBibtex.cpp:21:
../../../../src/Encoding.h: In member function ‘std::vector<std::basic_string<unsigned int, std::char_traits<unsigned int>, std::allocator<unsigned int> > > lyx::CharInfo::textCommands() const’:
../../../../src/Encoding.h:82:62: error: could not convert ‘((const lyx::CharInfo*)this)->lyx::CharInfo::text_commands_’ from ‘vector<lyx::trivial_string<unsigned int>>’ to ‘vector<std::basic_string<unsigned int, std::char_traits<unsigned int>, std::allocator<unsigned int> >>’
   82 |         std::vector<docstring> textCommands() const { return text_commands_; }
      |                                                              ^~~~~~~~~~~~~~
      |                                                              |
      |                                                              vector<lyx::trivial_string<unsigned int>>
../../../../src/Encoding.h: In member function ‘std::vector<std::basic_string<unsigned int, std::char_traits<unsigned int>, std::allocator<unsigned int> > > lyx::CharInfo::mathCommands() const’:
../../../../src/Encoding.h:86:62: error: could not convert ‘((const lyx::CharInfo*)this)->lyx::CharInfo::math_commands_’ from ‘vector<lyx::trivial_string<unsigned int>>’ to ‘vector<std::basic_string<unsigned int, std::char_traits<unsigned int>, std::allocator<unsigned int> >>’
   86 |         std::vector<docstring> mathCommands() const { return math_commands_; }
      |                                                              ^~~~~~~~~~~~~~
      |                                                              |
      |                                                              vector<lyx::trivial_string<unsigned int>>

-- 
Enrico