C: add -fwalkall to -O2

also walksyms for all forced packages, not just prev. deleted ones.

Try to fix issue27-1: perlcc -O2 -r -e"require LWP::UserAgent;print q(ok);"
where late adding of Config when adding DynaLoader misses to add the Config syms.

walkall recursively walks all outstanding packages'
C: move -fno-walkall from -O3 to -O1

only -O0 does now walkall