[asan] add option to set shadow mapping offset

Allowing overriding the default ASAN shadow mapping offset with the
-asan-shadow-offset option, and allow zero to be specified for both offset and
scale.

Patch by Aaron Carroll <aaronc@apple.com>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268724 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed