Fix build with newer newlib

avoid non-standard predefined macros

Fix ld.so load address at 4 KiB

Acquire write permissions before zeroing page in ELF loader

f81b722bf004177eadaf6f1b4b9e699e20257521 is a regression. If a
read-only segment does not begin on a page boundary, it would cause
the ELF loader to blow up.

make sure pages for ELF sections have correct protection (#40)

Disallow execution of RVC binaries on non-RVC pk

Use panic, not die, to terminate elf loader

Refactor pk, bbl, machine into separate libraries

Yuck.

Disentangle PK and BBL a bit

Remove incorrect code supporting ELF32 on RV64 and vice-versa

This is technically possible by running an RV32 supervisor on an
RV64 machine, but the M-mode and S-mode code would need to be
compiled and linked separately.

Fix loading of misaligned ELF segments

Update to new privileged spec

Relocate binaries that conflict with the pk's address space

Of course, this is only possible for PIEs, e.g. the dynamic linker.

Abandon MIPS convention for indicating syscall errors in register a3

Update to new privileged ISA

Support Linux ABI and (optionally) virtual memory

add BSD license

add clean-room elf.h to avoid GPL entanglement

temporary undoing of renaming

Renamed packages

[pk] fixed elf loader

[pk] made PK smaller

[sim,pk] fixed minor pk bugs and trap codes

[pk,fesvr] pk now loads elfs itself

this allows it to detect 32b binaries