[compiler-rt] [compiler-rt] Do not assume pthread_key_t to be a scalar type. (PR #70786)

[A. Jiang via llvm-commits]

https://github.com/frederick-vs-ja commented:

I think we should use `= {}` for clarity. (Perhaps we can/should even omit `=`.)

https://github.com/llvm/llvm-project/pull/70786