emulators/virtualbox-ose{,-nox11,-kmod,-additions,-additions-nox11}-legacy: fix build with llvm15+, fix run with PAE on i386

• Fix build with llvm15+ from ports and from base:
  • ISO C++17 does not allow 'register' storage class specifier;
  • require -fPIC on i386.
• Fix load kernel modules on host and guest i386 if kernel compiled with

PAE option: add non-default option PAE to ports.
Based on patches from mi@.

PR: 279257 224616
Approved by: vbox (maintainer, timeout 1 month and 6 years)