Change subexpressions to be visited in the CFG from left-to-right.

This is a more natural order of evaluation, and it is very important
for visualization in the static analyzer.  Within Xcode, the arrows
will not jump from right to left, which looks very visually jarring.
It also provides a more natural location for dataflow-based diagnostics.

Along the way, we found a case in the analyzer diagnostics where we
needed to indicate that a variable was "captured" by a block.

-fsyntax-only timings on sqlite3.c show no visible performance change,
although this is just one test case.

Fixes <rdar://problem/13016513>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174447 91177308-0d34-0410-b5e6-96231b3b80d8
Minor tweak to install docs

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174448 91177308-0d34-0410-b5e6-96231b3b80d8
Add note why we used a switch.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174449 91177308-0d34-0410-b5e6-96231b3b80d8