[common] disable_warnings: sync clang ignores to gcc
[cmake] debug flags fixup for icc
[common] fixes a few shadowing warnings
[grid.walker] fixes base classes w/o virt dtors
[common.disable_warnings] corrects gcc guard
makes a bunch of single arg ctors explicit

afaict nothing is relying on the implicit type conversions
[la] adds vectorinterface note
fixes a few more warnings