[cmake io] Force /O3 on TStreamerInfo::ReadBuffer:
[cmake io] Force /O3 on TStreamerInfo::ReadBuffer:

At O0, all variables of all local scopes get separately allocated on the stack.
This sums up to 6k; streaming e.g. a RooWorkspace has 100s of recursions of this
function. Force O3, where the stack size shrinks to just above 200 bytes.

root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,root-mirror/root,olifre/root,olifre/root,olifre/root,karies/root,root-mirror/root,karies/root,karies/root,root-mirror/root,karies/root,olifre/root,karies/root,olifre/root,root-mirror/root,olifre/root,karies/root,olifre/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,olifre/root,karies/root,root-mirror/root,karies/root