[compiler-rt][ubsan] Split Implicit Integer Truncation Sanitizer into unsigned and signed checks

Summary:
This is compiler-rt part.
clang part is D50901.

Reviewers: rsmith, vsk, filcab, Sanitizers

Reviewed by: filcab

Differential Revision: https://reviews.llvm.org/D50902

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@344231 91177308-0d34-0410-b5e6-96231b3b80d8
17 files changed