makefile: install dyn_start + dyn_stop

these files are mandatory with WANT_DYNAMIC which is the default now
stackgap: added some const annotations
fixup! Support for dynamic PAGE_SIZE

moved some code into find_in_auxvec() so that number of changes and
#ifdef can be reduced

Signed-off-by: Enrico Scholz <enrico.scholz@ensc.de>
stackgap: moved 'myrand[]' to outer scope

The address of 'myrand[]' will be used later in the outer scope so
that this buffer should by allocated there too.

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