specify windows-msvc compiler flags

[cartercanedy]

On windows, statically linking libjpeg-turbo in release builds resulted in extremely poor performance relative the system-provided shared library. Inspecting the cmake output showed that there weren't any optimization flags specified. This should fix windows-specific performance, but it's also possible that all platforms have the same behavior.

[honzasp]

Hmm, the cmake crate has some logic that should automatically pick the CMake profile from the Rust opt level:
https://docs.rs/cmake/latest/cmake/struct.Config.html#method.profile

And the TurboJPEG build guide doesn't mention that manually setting optimization flags for the compiler should be necessary, they just say that CMake should be run with -DCMAKE_BUILD_TYPE=Release:
https://github.com/libjpeg-turbo/libjpeg-turbo/blob/main/BUILDING.md#visual-c-command-line

When building for x86_64-unknown-linux-gnu on my system, I verified that the build script calls cmake with -DCMAKE_BUILD_TYPE=Release and that the generated Makefiles do build the static library with -O3. I don't have access to a Windows system at the moment, can you please check where this breaks on your system? In particular, does the build script call cmake with a correct -DCMAKE_BUILD_TYPE? (You can see the cmake arguments in the output of the build script, which you can see by invoking cargo with -vv)