Fix PR 9626 (duplicated self-init warnings under -Wuninitialized) with numerous CFG...

Fix PR 9626 (duplicated self-init warnings under -Wuninitialized) with numerous CFG and UninitializedValues analysis changes:

1) Change the CFG to include the DeclStmt for conditional variables, instead of using the condition itself as a faux DeclStmt.
2) Update ExprEngine (the static analyzer) to understand (1), so not to regress.
3) Update UninitializedValues.cpp to initialize all tracked variables to Uninitialized at the start of the function/method.
4) Only use the SelfReferenceChecker (SemaDecl.cpp) on global variables, leaving the dataflow analysis to handle other cases.

The combination of (1) and (3) allows the dataflow-based -Wuninitialized to find self-init problems when the initializer
contained control-flow.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@128858 91177308-0d34-0410-b5e6-96231b3b80d8