Fix PR7402: We were creating implicit member initializers for every field in an

anonymous union under the presumption that they didn't do anything. While this
is true, our checks for redundant initialization of an anonymous union still
fire when these overlap with explicit user initialization. A cleaner approach
is to avoid initializing multiple members of a union altogether, but this still
is in a rather fuzzy are especially when C++0x allows non-POD types into
unions.

llvm-svn: 107235