New comment by yopito on void-packages repository

https://github.com/void-linux/void-packages/pull/26962#issuecomment-765610902

Comment:
Since qt5 is built with gcc, adding `-isystem /usr/armv7l-linux-gnueabihf/usr/include/c++/10.2/armv7l-linux-gnueabihf` to clang make it happy !
manual build once packaging failed as usual:
```
(chroot) $ clang --target=armv7l-linux-gnueabihf --sysroot=/usr/armv7l-linux-gnueabihf \
                          -fPIC -Wno-constant-logical-operand -std=c++14  \
                          -I/usr/armv7l-linux-gnueabihf/usr/include/qt5 \
                          -isystem/usr/armv7l-linux-gnueabihf/usr/include/c++/10.2/armv7l-linux-gnueabihf \
                           /tmp/QtCore_global_XSznox.hpp

=> no error, a .gch file has been generated:

/tmp/QtCore_global_XSznox.hpp
/tmp/QtCore_global_XSznox.hpp.gch
```
Related to gcc internals for C++, its equivalent of clang's systoot I guess ?
Keep on digging