[analyzer] Prune calls to functions with linear CFGs that return a non-zero constrain...

[analyzer] Prune calls to functions with linear CFGs that return a non-zero constrained value

During the evaluation of D62883, I noticed a bunch of totally
meaningless notes with the pattern of "Calling 'A'" -> "Returning value"
-> "Returning from 'A'", which added no value to the report at all.

This patch (not only affecting tracked conditions mind you) prunes
diagnostic messages to functions that return a value not constrained to
be 0, and are also linear.

Differential Revision: https://reviews.llvm.org/D64232

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@368771 91177308-0d34-0410-b5e6-96231b3b80d8