[ASan] Cache the OSX version to avoid calling sysctl() on every GetMacosVersion() call.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@186389 91177308-0d34-0410-b5e6-96231b3b80d8
[ASan] Use less shadow on Win 32-bit

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@186393 91177308-0d34-0410-b5e6-96231b3b80d8