[ubsan] Mark overflow checks with !nosanitize

Sanitizer instrumentation generally needs to be marked with !nosanitize,
but we're not doing this properly for ubsan's overflow checks.

r213291 has more information about why this is needed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@302598 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit d9b4d2283a86ba0ed2a768f3d012ba4ee1859eab)
2 files changed