[inductor] fix UndefinedTensorImpl singleton can't export on Windows.

[xuhancn]

This PR fix the UndefinedTensorImpl::_singleton can't export on Windows issue.
Snapshot:

The reason is MSVC can't export class static data to external linkage, ref: https://learn.microsoft.com/en-us/cpp/cpp/using-dllimport-and-dllexport-in-cpp-classes?view=msvc-170#_pluslang_using_dllimport_and_dllexport_in_c2b2bselectivememberimportexport

I use another singleton implenmentation to avoid the issue, for Windows.

Since this PR, cpp_wrapper on Windows would start to work.

Next step, I will enable the cpp_wrapper UTs.

cc @peterjc123 @mszhanyi @skyline75489 @nbcsm @iremyux @Blackhex @jgong5 @mingfeima @XiaobingSuper @sanchitintel @ashokei @jingxu10 @voznesenskym @penguinwu @EikanWang @Guobing-Chen @zhuhaozhe @blzheng @wenzhe-nrv @jiayisunx @ipiszy @yf225 @chenyang78 @kadeng @muchulee8 @ColinPeppler @amjames @desertfire @chauhang

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[jgong5]

Can we do getInstance() regardless of whether it is MSVC build or not?

[xuhancn]

Can we do getInstance() regardless of whether it is MSVC build or not?

460143f getInstance() will fail with constexpr on non-Windows OS.

[desertfire]

The doc you linked suggests using dllexport (C10_EXPORT in PyTorch) would solve the problem. Have you tried that?

[xuhancn]

The doc you linked suggests using dllexport (C10_EXPORT in PyTorch) would solve the problem. Have you tried that?

@desertfire
I tried the C10_EXPORT for the variable, and It doesn't work, I checked with dumpbin, and confirmed. class static variable is not exported by C10_EXPORT.

[xuhancn]

@pytorchbot merge

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