gcc that comes with Bela does support that, though
I tried to build the library, and after hacking my way into convincing it to build it anyhow, it still fails at
string_view. This was allegedly supported as experimental by
g++-6.3 that is on the board, but including the experimental headers make the build crash in an even worse way. Replacing the one instance of
std::string makes it work anyhow.
Interestingly, building it is not actually needed because
q_lib is a no-frills, lightweight, header-only library.
which means you should be able to use it without building anything, just point your project to the relevant includes, almost as you have done above:
CPPFLAGS= -I/root/Bela/projects/qPitchSynth/q/q_lib/include -I/root/Bela/projects/qPitchSynth/infra/include;
see if you still see C++17-related errors.
The issue you had with "undefined reference" was probably because as part of your project you had included the files from
q_io which are not actually needed.