OSv fails to build on Fedora 36

[nyh]

OSv fails to compile on Fedora 36 (which, among other things, has gcc 12.1.1).
Some of the errors:

include/osv/sched.hh:353:30: error: field ‘_name’ has incomplete type ‘std::array<char, 16>’
  353 |         std::array<char, 16> _name = {};
      |                              ^~~~~

./bsd/sys/sys/queue.h:591:26: error: storing the address of local variable ‘tb’ in ‘*queue.tq_active.tqh_last’ [-Werror=dangling-pointer=]
  591 |         (head)->tqh_last = &TAILQ_NEXT((elm), field);                   \
      |                          ^

./drivers/pci-function.hh:360:28: error: ‘template<class _Arg, class _Result> struct std::unary_function’ is deprecated [-Werror=deprecated-declarations]
  360 |         struct hash : std::unary_function< const function*, std::size_t> {
      |                            ^~~~~~~~~~~~~~

[nyh]

I just committed six patches that fix several compilation errors on Fedora 36 (gcc-12.1.1-1.fc36.x86_64), but unfortunately several more problems remain, in the following source files:

musl/src/time/__year_to_secs.c
musl/src/math/__rem_pio2_large.c
bsd/sys/xen/evtchn.cc
fs/virtiofs/virtiofs_dax.cc
bsd/sys/dev/hyperv/vmbus/hyperv.cc

The last file even crashes the compiler...

[nyh]

After several more patches, all compilation succeeds but the linking fails: getentropy() is missing, and libstdc++.a apparently started to use it if built with getentropy() available on the build machine (see https://gcc.gnu.org/pipermail/gcc-cvs/2021-November/356441.html)