QtLocations 5.15.0 alpha fails to build in C+20 mode (using clang10, but any other compliant compiler should react the same way) because of pre-C+20 code in the old versions of boost and earcut.

Updating src/3rdparty/mapbox-gl-native/deps/boost to boost 1.72.0 [or, better yet, not bundling boost and using the system version instead] and src/3rdparty/mapbox-gl-native/deps/earcut to earcut to the version in earcut git https://github.com/mapbox/earcut.hpp/blob/master/include/mapbox/earcut.hpp
solves both problems.

Also, src/3rdparty/mapbox-gl-native/platform/default/bidi.cpp needs to #include <stdexcept> to get std::runtime_error and src/3rdparty/mapbox-gl-native/src/mbgl/util/convert.cpp needs to #include <cstdint> to get int32_t.