copysign function misbehaves in Windows

[auto-differentiation-dev]

Describe the bug

As can be seen in this CI build of QuantLib-Risks-Cpp, the copysign function from XAD does not get called correctly in Windows on this line: https://github.com/lballabio/QuantLib/blob/master/test-suite/basketoption.cpp#L1793

To Reproduce

Build QuantLib-Risks-Cpp in Windows with Visual Studio, using QuantLib's master branch.

Expected behaviour

The code should compile.

Environment:

• OS: Windows
• Compiler: VC++ 2022 (toolset 14.4)

Additional context

This is best solved by first reproducing the problem in an XAD unit test.