runtime/race package contains the data race detector runtime library.
It is based on ThreadSanitizer race detector, that is currently a part of
the LLVM project (http://llvm.org/git/compiler-rt.git).
To update the .syso files use golang.org/x/build/cmd/racebuild.
Current runtime is built on rev e35e7c00b5c7e7ee5e24d537b80cb0d34cebb038.