tree-optimization/120729 - limit compile time in uninit_analysis::prune_phi_opnds

tree-optimization/120729 - limit compile time in uninit_analysis::prune_phi_opnds

The testcase in this PR shows, on the GCC 14 branch, that in some
degenerate cases we can spend exponential time pruning always
initialized paths through a web of PHIs.  The following adds
--param uninit-max-prune-work, defaulted to 100000, to limit that
to effectively O(1).

	PR tree-optimization/120729
	* gimple-predicate-analysis.h (uninit_analysis::prune_phi_opnds):
	Add argument of work budget remaining.
	* gimple-predicate-analysis.cc (uninit_analysis::prune_phi_opnds):
	Likewise.  Maintain and honor it throughout the recursion.
	* params.opt (uninit-max-prune-work): New.
	* doc/invoke.texi (uninit-max-prune-work): Document.