Consider disabling -Wunused-parameter in compilation

[stephentu]

I switched over from gcc to clang for my default C++ compiler, and clang is pretty verbose by default about unused parameters.

We can either fix these warnings or compile with -Wno-unused-parameter. Either is fine by me, but I'm more inclined towards the latter since I think unused parameters is no big deal.

[rcurtin]

In 3ad083b I've fixed the -Wunused-parameter warnings. They don't appear under gcc, but I think this may be because gcc might not issue warnings for functions it isn't actually compiling into something. Just a guess though. I fixed some -Wunused-private-field warnings in fba66e1 and 660fd96. With those fixes, do you still see warnings? (Maybe at the level of Armadillo?)

Personally I like fixing warnings, in case downstream projects are compiling with aggressive warning settings (I think RcppMLPACK compiles with -pedantic? I'm not certain though).

[stephentu]

Ok, clang is now quiet on a clean build. Thanks! Closing this issue.