`xvalues.cpp`: Remove unused non-constant "constants" in vNext

[AlexGuteniev]

This machinery is DLL-exported but unused:

STL/stl/src/xvalues.cpp

Lines 19 to 38 in cbe2ee9

	// TRANSITION, ABI: preserved for binary compatibility
	union _Dconst { // pun float types as integer array
	unsigned short _Word[8];
	float _Float;
	double _Double;
	long double _Long_double;
	};
	extern _CRTIMP2_PURE _Dconst _Denorm = {1, 0, 0, 0};
	extern _CRTIMP2_PURE _Dconst _LDenorm = {1, 0, 0, 0};
	extern _CRTIMP2_PURE _Dconst _Hugeval = {0, 0, 0, 0x7ff0};
	extern _CRTIMP2_PURE _Dconst _Inf = {0, 0, 0, 0x7ff0};
	extern _CRTIMP2_PURE _Dconst _LInf = {0, 0, 0, 0x7ff0};
	extern _CRTIMP2_PURE _Dconst _Nan = {0, 0, 0, 0x7ff8};
	extern _CRTIMP2_PURE _Dconst _LNan = {0, 0, 0, 0x7ff8};
	extern _CRTIMP2_PURE _Dconst _Snan = {1, 0, 0, 0x7ff0};
	extern _CRTIMP2_PURE _Dconst _LSnan = {1, 0, 0, 0x7ff0};
	extern _CRTIMP2_PURE _Dconst _FDenorm = {1, 0};
	extern _CRTIMP2_PURE _Dconst _FInf = {0, 0x7f80};
	extern _CRTIMP2_PURE _Dconst _FNan = {0, 0x7fc0};
	extern _CRTIMP2_PURE _Dconst _FSnan = {1, 0x7f80};

vNext note: Resolving this issue will require breaking binary compatibility. We won't be able to accept pull requests for this issue until the vNext branch is available. See #169 for more information.

[frederick-vs-ja]

Some internal functions are no longer used and not DLL-exported. Can we drop them right now?

[StephanTLavavej]

A. Jiang (@frederick-vs-ja) Yes, but you have to be very careful about searching for usage. Some of them are cleverly macroized for float/double/long double variants, so the identifiers appear to be unused at first.

[StephanTLavavej]

#5836 radically simplified this, so the remaining work in vNext will be trivial.