[sanitizer] Fix off-by-8x in direct coverage.

File mapping offset was calculated by offsetting (uptr *) instead of (char *).


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@224821 91177308-0d34-0410-b5e6-96231b3b80d8
[sanitizer] Disable InternalMmapWithOffset test on OSX.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@224822 91177308-0d34-0410-b5e6-96231b3b80d8