[CMake] Off-topic? Winmm linking/running problems

[Gonzalo Garramuño]

I have a multiplatform viewer and recently I started to experience some 
very weird behavior.
I am using the latest cmake 3.5.3 rc1 and the latest released ninja 
(1.7), albeit the problem appears with NMake Makefiles too.
The viewer links against winmm.dll, the windows multimedia library for 
audio.  I am using ffmpeg to decode the audio with /OPT:NOREF.

My problem is that the win64 version of my program, while testing in the 
sandbox, plays all audio in mono.
The win32 version of my program (same code) works fine from the sandbox.
Also, when I move the win64 version of the program (doing ninja install, 
package install or even just a plain cp to a new tree), the same win64 
version of my program plays audio (stereo, 5:1) just fine.
The linux amd64 version of my program also plays audio just fine without 
installing.
All the code lies in an NTFS partition.

I am at a loss as to what might the problem be.  I am pretty sure all 
variables are initialized properly and that there's no memory issue, but 
you never know.  I have no spaces in the paths.  It is not a driver 
issue as some other user reported mono playback too.  I was wondering if 
someone has experienced anything like this and how to debug it.