Support using llvm-libunwind
This commit adds support for using llvm-libunwind for kernels built
using llvm and clang. The two differences are that the largest register
index is given by _LIBUNWIND_HIGHEST_DWARF_REGISTER, we need to check
whether the register is a floating point register and the prototype
for unw_regname takes the unwind cursor as the first argument.
Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Sebastian Pauka <me@spauka.se>
Closes #17230