[sanitizer] fix the GetBlockBegin overflow bug while preserving the performance optimization (use 32-bit division when possible). Improve the benchmarks that checks for performance of GetBlockBegin/GetMetaData

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@181989 91177308-0d34-0410-b5e6-96231b3b80d8
[asan] fix ShadowGapTest on PowerPC64

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@181991 91177308-0d34-0410-b5e6-96231b3b80d8