Complete support for C++ Core Guidelines Type.6: Always initialize a member variable.

Summary: Added the remaining features needed to satisfy C++ Core Guideline Type.6: Always initialize a member variable to cppcoreguidelines-pro-type-member-init. The check now flags all default-constructed uses of record types without user-provided default constructors that would leave their memory in an undefined state. The check suggests value initializing them instead.

Reviewers: flx, alexfh, aaron.ballman

Subscribers: klimek, aaron.ballman, LegalizeAdulthood, cfe-commits

Patch by Michael Miller!

Differential Revision: http://reviews.llvm.org/D18584

llvm-svn: 266191