[CMake branch] Clang support on windows

[MeijisIrlnd]

Hiya, when trying to use a Clang toolchain on Windows on the cmake branch, compilation fails due to /Zi being present, which under an msvc-like frontend, generates pdb files.
I had a bit of a rummage around, and found that /Zi is hardcoded in the current iplug_configure_target implementation - I was able to get it working by checking if the compiler's cli is msvc-like or not, and if not, replacing /Zi with -DEBUG in clang's case.
Not sure if this is a viable solution for g++, but it works with Clang on windows, I'll link the PR with the fix to this issue,
Hope it's at-all useful!