[asan] Switch initialization to "double-checked locking"

This allows to remove `asan_init_is_running` which likely had a data
race.

Simplifies https://github.com/llvm/llvm-project/pull/74086 and reduces a difference between platforms.

Reviewers: zacklj89, eugenis, dvyukov

Reviewed By: zacklj89, dvyukov

Pull Request: https://github.com/llvm/llvm-project/pull/74387