In theory, it should be possible to cross-compile to a Windows target on a Linux build system, using the wine Win32 API emulator.

This has been done by other projects, such as https://github.com/mstorsjo/msvc-wine.

Building on Linux, even when going through wine, is likely to produce a performance boost. (The rationale is that the compiler does not make much use of the OS so the Wine emulation overhead is low, while the better IO on Linux is presumably going to help.) But an even more important aspect is that it would allow developers running a Linux desktop to quickly build a Windows version, to verify that they have introduced no build breakage.

(In theory, even tests should be able to run through wine, but that is likely to have a very different cost/benefit situation.)