ARM: call the stackgap code in _start

This was missing for EABI and required for new TLS code which does
some initialization there.

Signed-off-by: Enrico Scholz <enrico.scholz@ensc.de>
fixup! ARM: updated unified.S to compile with recent TLS changes

minor whitespace cleanups

Signed-off-by: Enrico Scholz <enrico.scholz@ensc.de>
ARM: implemented TLS startup code

doing it in the stackgap initialization is hacky but done in upstream
code so we do it for ARM too.

Signed-off-by: Enrico Scholz <enrico.scholz@ensc.de>
fixup! gitignore: initial checkin

added autogenerated errno header

Signed-off-by: Enrico Scholz <enrico.scholz@ensc.de>