[clang] P2266 implicit moves STL workaround

This patch replaces the workaround for simpler implicit moves
implemented in D105518.

The Microsoft STL currently has some issues with P2266.

Where before, with -fms-compatibility, we would disable simpler
implicit moves globally, with this change, we disable it only
when the returned expression is in a context contained by
std namespace and is located within a system header.

Signed-off-by: Matheus Izvekov <mizvekov@gmail.com>

Reviewed By: aaron.ballman, mibintc

Differential Revision: https://reviews.llvm.org/D105951