Fix strict-aliasing issues with _strtod_r and Storeinc.

	Fix strict-aliasing issues with _strtod_r and Storeinc.
	* libc/stdlib/strtod.c (_strtod_r): Change local variables aadj,
	rv, rv0 from double to type U.  Use accessor macros dval, dword0
	and dword1 for all accesses except for the ULtod call, where rv.i
	replaces the pointer cast.
	* libc/stdlib/mprec.h (U): Rename member L to i for easier re-use
	of access macros.  Tweak comment.
	Remove #ifdef'd YES_ALIAS code.
	(dword0, dword1, dval): Define in terms of uncast union member
	access.  Ditto for _DOUBLE_IS_32BITS variants.
	(Storeinc): Replace aliasing-flawed microoptimized definition with
	alternative suggested in comment.  Remove now stale comment.