Fix compilation errors.

[dan-zheng]

This is a follow-up to #119, which I accidentally merged without testing.

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• Fix VJPs for maxPooled3D and averagePooled3D.
• Temporarily, fix tests to use SimpleRNNCell.State.

[dan-zheng]

cc @Shashi456: this fixes compilation errors from #119.

There's one remaining test failure, which requires a compiler patch:

$ swift test
duplicate symbol _AD__orig_$s10TensorFlow0A0VAASjRzrlE1moiyACyxGAE_AEtFZ_$s10TensorFlow0A0VyxGA2DXMtA4DIegggo_Iegggyoo_A3DXMtA3DIeggo_Iegggyoo_AA0aB13FloatingPointRzlTR_src_0_wrt_0_jvp_thunk in:
    /Users/danielzheng/swift-apis/.build/x86_64-apple-macosx/debug/DeepLearning.build/Layer.swift.o
    /Users/danielzheng/swift-apis/.build/x86_64-apple-macosx/debug/DeepLearning.build/Loss.swift.o
duplicate symbol _AD__orig_$s10TensorFlow0A0VAASjRzrlE1moiyACyxGAE_AEtFZ_$s10TensorFlow0A0VyxGA2DXMtA4DIeggoo_Iegggyoo_A3DXMtA3DIeggo_Iegggyoo_AA0aB13FloatingPointRzlTR_src_0_wrt_0_vjp_thunk in:
    /Users/danielzheng/swift-apis/.build/x86_64-apple-macosx/debug/DeepLearning.build/Layer.swift.o
    /Users/danielzheng/swift-apis/.build/x86_64-apple-macosx/debug/DeepLearning.build/Loss.swift.o
ld: 2 duplicate symbols for architecture x86_64
error: link command failed with exit code 1 (use -v to see invocation)
[0/1] Linking DeepLearningPackageTests

I can land a PR for that soon, but it will take some time for a new toolchain to become available.

[Shashi456]

Thanks a lot for fixing it @dan-zheng, I should've experimented with the ksize and strides a little to understand what went wrong. So will you revert #119 or patch this and your proposed PR in?

[dan-zheng]

So will you revert #119 or patch this and your proposed PR in?

I'll merge this patch PR now instead of reverting #119. I'll update you when the duplicate symbol linker error fix is ready.

[dan-zheng]

Tested locally.
Compilation works for swift test, but there's a duplicate symbol error as shown above. Fixing that requires a compiler patch - coming soon.