libstdc++: Use 128-bit arithmetic for std::linear_congruential_engine [PR87744]

For 32-bit targets without __int128 we need to implement the LCG
transition function by hand using 64-bit types.

We can also slightly simplify the __mod function by using if-constexpr
unconditionally, disabling -Wc++17-extensions warnings with diagnostic
pragmas.

libstdc++-v3/ChangeLog:

	PR libstdc++/87744
	* include/bits/random.h [!__SIZEOF_INT128__] (_Select_uint_least_t):
	Define specialization for 64-bit generators with
	non-power-of-two modulus and large constants.
	(__mod): Use if constexpr unconditionally.
	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error
	line number.
	* testsuite/26_numerics/random/linear_congruential_engine/87744.cc:
	New test.