Fix All Compile Warnings. about opus

[wiiaboo]

GCC build in Travis has only two warnings: https://travis-ci.org/xiph/opus/jobs/176869299#L675-L677
32-bit VS2015 Release has 26 warnings and 64-bit VS2015 Release has 31. A few of these are in silk fixed files which aren't even used if FIXED_POINT isn't defined.
32-bit and 64-bit VS2015 ReleaseDLL builds don't have as much warnings because they don't compile these FIXED_POINT files.

[jmvalin]

Every version of every compiler warns about different things, so we can't "fix all compile warnings". We can fix particular warnings, but that requires information about the exact warning, where it's reported, and (often) why it's reported (what the compiler "thinks" is wrong).

[jmvalin]

Are there still warnings that need fixing or should we close this?

[AraHaan]

Ok, time to build to see if the compile warnigns are all resolved.