libstdc++: Merge latest Ryu sources

libstdc++-v3/ChangeLog:

	* src/c++17/ryu/MERGE: Update the commit hash.
	* src/c++17/ryu/d2s_intrinsics.h: Merge from Ryu's master
	branch.

Signed-off-by: Patrick Palka <ppalka@redhat.com>