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GH-35596: [C++][CI] Improve compilation caching with PCG (#35597)


### Rationale for this change

The PCG headers use the `__DATE__` and `__TIME__` macros, which makes builds non-deterministic:
https://github.com/imneme/pcg-cpp/issues/59

Deterministic builds are useful for a number of reasons. One is security audits of binary artifacts, another (that directly affects us) is making compilation caching as efficient as possible. Preprocessor-based compilation caching breaks when time-dependent macros are used.

### What changes are included in this PR?

Remove the `struct static_arbitrary_seed` construct from PCG.
Also, enable a gcc/clang warning that detects the use of non-deterministic preprocessor macros.

### Are these changes tested?

Yes, by the additional warning (which is turned into an error in "checkin" warnings mode).

### Are there any user-facing changes?

No.

* Closes: #35596

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>