build: add gcc <9.1 and clang <9.0 compatibility

[AndreCostaaa]

Encountered a linking issue when using an old GCC version:

/home/andre/dev/lvgl/lv_port_linux/build/_deps/fastgltf-src/src/io.cpp:442: undefined reference to `std::filesystem::file_size(std::filesystem::__cxx11::path const&, std::error_code&)'
/opt/poky/3.1.33/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/8.3.0/real-ld: _deps/fastgltf-build/libfastgltf.a(io.cpp.o): in function `fastgltf::Parser::loadFileFromUri(fastgltf::URIView&) const':
/opt/poky/3.1.33/sysroots/aarch64-poky-linux/usr/include/c++/8.3.0/bits/fs_path.h:257: undefined reference to `std::filesystem::__cxx11::path::has_filename() const'
/opt/poky/3.1.33/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/8.3.0/real-ld: /opt/poky/3.1.33/sysroots/aarch64-poky-linux/usr/include/c++/8.3.0/bits/fs_path.h:260: undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
/opt/poky/3.1.33/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/8.3.0/real-ld: /opt/poky/3.1.33/sysroots/aarch64-poky-linux/usr/include/c++/8.3.0/bits/fs_path.h:260: undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
/opt/poky/3.1.33/sysroots/x86_64-pokysdk-linux/usr/libexec/aarch64-poky-linux/gcc/aarch64-poky-linux/8.3.0/real-ld: lvgl/lib/liblvgl.a(lv_gltf_data_injest.cpp.o): in function `create_data_from_bytes(unsigned char const*, unsigned long)':
/opt/poky/3.1.33/sysroots/aarch64-poky-linux/usr/include/c++/8.3.0/bits/fs_path.h:184: undefined reference to `std::filesystem::__cxx11::path::_M_split_cmpts()'
collect2: error: ld returned 1 exit status

cppreference mentions having to link with stdc++fs for GCC and c++fs for clang: https://en.cppreference.com/w/cpp/filesystem.html#Notes

[spnda]

I guess this is fair, however be mindful that #116 will break compatibility with anything below GCC 10 and LLVM 10.

This was one of the concerns I had with lvgl using fastgltf, since embedded has a major problem with outdated toolchains in my opinion and I don't want that dragging this library behind. I want to merge #116 for 0.10 which means that this change will only live in 0.9.x and will be removed again for the next version.