Perform array bounds checking in more situations and properly handle special

Perform array bounds checking in more situations and properly handle special
case situations with the unary operators & and *. Also extend the array bounds
checking to work with pointer arithmetic; the pointer arithemtic checking can
be turned on using -Warray-bounds-pointer-arithmetic.

The changes to where CheckArrayAccess gets called is based on some trial &
error and a bunch of digging through source code and gdb backtraces in order
to have the check performed under as many situations as possible (such as for
variable initializers, arguments to function calls, and within conditional in
addition to the simpler cases of the operands to binary and unary operator)
while not being called--and triggering warnings--more than once for a given
ArraySubscriptExpr.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@136997 91177308-0d34-0410-b5e6-96231b3b80d8