After painstaking 5 days, compiling the Viewer up and down, back and forth and trying to find the issue, i finally, randomly stumbled upon the solution by "trying something really stupid". Needless to say stupid sadly wins. I managed to compile the Viewer as 64bit executable, with sound and texture decoding intact.
You can download the 64bit version on the usual downloads page of bitbucket. Please not that this 64bit version is absolutely the same as the 32bit version except that it is now obviously 64bit. From my tests so far however i can tell you that it runs a lot faster (for me) than the 32bit version ever did. I'm talking about 20+ more fps on the above picture's place and 10-20 more fps in the place on the picture below.
This is a drastic improvement, make sure that texture loading is done before comparing your fps, while textures where still downloading i got roughly the same low 10 fps but when they were done loading i went up to rock solid 25-30 fps. That's with deferred, shadows and SSAO on.
This build also rips out the updater system which allows the Viewer to start up faster, login a bit faster and eliminates the freeze whenever you open Dragon - Help - About Black Dragon. However, this build doesn't come with the launcher nor updater, i'll have to reconfigure them for Black Dragon soon so they'll keep it updated, so you'll have to update it manually for the time being until i can get the launcher working and can verify that its updating the Viewer properly.
For now however i'll need some rest. A lot of rest. 5 days nonstop headache trying to fix this mess just so it turns out it's a "stupid thing" that fixed it. Ugh. Oz. Get your goddamn documentation together. If you had like written one single sentence, one simple "note that 64bit libs are named after their 32bit counterparts while the dll's are named 64 as usual" all this mess could have been skipped. Or at least give us some sort of insight into your building process for the libraries like fmodex because as you may know OR NOT, we can't look into them because we cannot get them, we have to build them ourselves, which if there is no documentation on how to actually build them, is a bit hard, you know.
Thanks to everyone who tried to help me solving this shit. Specifically Whirly, Nicky, Henri and Cinder. You might not have actually helped but at least you tried, that's what counts. Also thanks to my dad who installed all this crap to look into it just to fail as i did, he did a good job at mentally and morally supporting me with his failed attempts.