CMake fixes for WinAMP

[madebr]

With these fixes, I am able to let the WavPack Decoder plug-in appear in WinAMP. Proof:

• By adding the objects of wavpack to in_wv.dll instead of linking to it, you don't need to copy the wavpackdll.dll to the winamp folder. Copying wavpackdll.dll to the Plugins folder wasn't enough, you had to copy it to the folder containing the winamp executable. By embedding wavpack in in_wv.dll, there are no more external dependencies.
• Link to static libgcc and libstdc++ to avoid needing the GNU standard library in a public location.

I suppose cooledit suffers from similar issues.

[sezero]

By adding the objects of wavpack to in_wv.dll instead of linking to it, you don't need to copy the wavpackdll.dll

I think @dbry is linking the plugin to static libwavpack, but I may be wrong. However ...

Link to static libgcc and libstdc++ to avoid needing the GNU standard library in a public location.

... this may be the actual issue he has had. Otherwise, there is no reason that in_wv plugin to fail loading.

[madebr]

By adding the objects of wavpack to in_wv.dll instead of linking to it, you don't need to copy the wavpackdll.dll

I think @dbry is linking the plugin to static libwavpack, but I may be wrong. However ...

This issue does not exist with a static wavpack library indeed, but this solution works with both shared and static wavpack. So win win chicken dinner :)

[dbry]

This loads into winamp (as you show) but the dialogs (Configure, About, file info...) don't work because the resource file winamp/resource.rc was not included for in_wv. Once I added that the dialogs worked too! I'll push that change. Thanks!