[analyzer] Calculate liveness for symbolic exprs as well as atomic symbols.
[analyzer] Calculate liveness for symbolic exprs as well as atomic symbols.

No tests, but this allows the optimization of removing dead constraints.
We can then add tests that we don't do this prematurely.

<rdar://problem/12333297>

Note: the added FIXME to investigate SymbolRegionValue liveness is
tracked by <rdar://problem/12368183>. This patch does not change the
existing behavior.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@164621 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang