ASan: use dynamic lookup when building dynamic ASan runtime on Mac, because shadow mapping and offset are defined in the instrumented modules instead of runtime

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173015 91177308-0d34-0410-b5e6-96231b3b80d8
ASan: build runtime flexible mapping and offset in configure+make build as well

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173016 91177308-0d34-0410-b5e6-96231b3b80d8