LLVM not detected in bpfutil due to LLVM 16 requiring c++17

[No Name]

This is my first time reporting a bug, so apologies if I get something wrong.
In tools/build/feature/Makefile, line 342, the c++ std is set to
gnu++14, whereas LLVM 16 now requires c++17 to include the headers.
This results in the llvm feature being falsely disabled for bpfutil.
Perhaps the --cxxflags, --ldflags and --libs options of llvm-config
should instead?

Reagan.