Omit arguments of __builtin_object_size from the CFG.

This builtin does not actually evaluate its arguments for side effects,
so we shouldn't include them in the CFG. In the analyzer, rely on the
constant expression evaluator to get the proper semantics, at least for
now. (In the future, we could get ambitious and try to provide path-
sensitive size values.)

In theory, this does pose a problem for liveness analysis: a variable can
be used within the __builtin_object_size argument expression but not show
up as live. However, it is very unlikely that such a value would be used
to compute the object size and not used to access the object in some way.

<rdar://problem/14760817>

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188679 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Assume that strings are no longer than SIZE_MAX/4.

This keeps the analyzer from making silly assumptions, like thinking
strlen(foo)+1 could wrap around to 0. This fixes PR16558.

Patch by Karthik Bhat!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188680 91177308-0d34-0410-b5e6-96231b3b80d8
[analyzer] Add "unmodified variable" checker to the Potential Checkers.

This is PR16890.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188681 91177308-0d34-0410-b5e6-96231b3b80d8