Add a runtime method to find out if race detector is enabled

[anatol]

My version go version go1.17.1 linux/amd64

I have a code that needs to know whether the application runs with the race detector or not. In a way that is similar to testing.Verbose() tells whether -verbose flag is used.

I looked at public runtime library and did not find any method that allows to get information about the race detector. There is a SO question about it https://stackoverflow.com/questions/44944959/how-can-i-check-if-the-race-detector-is-enabled-at-runtime and it proposes a solution that uses buildtags. And there are many uses who follows this approach.

But it would be better if golang runtime library provided a cleaner way to find out if the race detector is enabled.

[ALTree]

Tracked in #36477, closing here in favour of the older thread. Feel free to subscribe/comment in that one.