WShadow is on for GCC and MSVC devs sometimes accidentally
add code emitting these warnings, since msvc does not warn
about this by default.
This patch enables the appropriate warnings, but it seems
to emit up quite a few warnings GCC somehow did not notice.
see P2228 for a list.
I don't necessarily need a code review it's more a of dicussion review
- Do we want to enable this?
- If so, can/should we tweak GCC to be more pro-active in this area
If we decide to land this, we should alteast resolve the outstanding
warnings before doing so.