[llvm] [OpenMPIRBuilder] Added `if` clause for `teams` (PR #69139)

[Kiran Chandramohan via llvm-commits]

kiranchandramohan wrote:

> The value of the argument must be an integer value. If the value evaluates to true (non-zero) integer, then the number of threads is determined by `num_threads` clause (or default and ICV if `num_threads` is absent). When the condition evaluates to false (zero), then the bounds are set to 1.

Is this mentioned in the standard? Or is it specific to the llvm openmp library? If the former, please add a pointer to the standard.

https://github.com/llvm/llvm-project/pull/69139