Remove TLI from isInTailCallPosition's arguments. NFC.

There is no need to pass on TLI separately to the function. As Eric pointed out
the Target Machine already provides everything we need.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213108 91177308-0d34-0410-b5e6-96231b3b80d8
Emit warnings if vectorization is forced and fails.

This patch modifies the existing DiagnosticInfo system to create a generic base
class that is inherited to produce diagnostic-based warnings. This is used by
the loop vectorizer to trigger a warning when vectorization is forced and
fails. Several tests have been added to verify this behavior.

Reviewed by: Arnold Schwaighofer


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213110 91177308-0d34-0410-b5e6-96231b3b80d8