libstdc++: Remove Ryu's uint128_t aliases

libstdc++: Remove Ryu's uint128_t aliases

This makes Ryu consistently use the uint128_t alias that's defined in
floating_to_chars.cc.

libstdc++-v3/ChangeLog:

	* src/c++17/ryu/LOCAL_PATCHES: Update.
	* src/c++17/ryu/d2s_intrinsics.h: Don't define uint128_t.
	* src/c++17/ryu/generic_128.h: Likewise.
	* src/c++17/ryu/ryu_generic_128.h (struct floating_decimal_128):
	Use uint128_t instead of __uint128_t.
	(generic_binary_to_decimal): Likewise.