libstdc++: Fix incorrect results in std::seed_seq::generate [PR 97311]

libstdc++: Fix incorrect results in std::seed_seq::generate [PR 97311]

This ensures that intermediate results are done in uint32_t values,
meeting the requirement for operations to be done modulo 2^32.

If the target doesn't define __UINT32_TYPE__ then substitute uint32_t
with a class type that uses uint_least32_t and masks the value to
UINT32_MAX.

I've also split the first loop that goes from k=0 to k<m into three
loops, for k=0, [1,s] and [s+1,m). This avoids branching for those three
cases in the body of the loop, and also avoids the concerns in PR 94823
regarding the k-1 index when k==0.

libstdc++-v3/ChangeLog:

	PR libstdc++/97311
	* include/bits/random.tcc (seed_seq::generate): Use uint32_t for
	calculations. Also split the first loop into three loops to
	avoid branching on k on every iteration, resolving PR 94823.
	* testsuite/26_numerics/random/seed_seq/97311.cc: New test.
	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-erro
	line number.