pcsx2: sign compare mismatch 1/3
pcsx2: sign compare mismatch 2/3
pcsx2: sign compare mismatch 3/3
pcsx2: remove useless volatile

Volatile is only useful as argument not the returned value
gsdx: remove/comment unused variable
pcsx2/plugin: sign compare mismatch extra
zzogl: bad function declaration
gcc warning: constify const string
gcc-warning: check c function return. Print error when bad.

v2: properly check return code of fread/getcwd function
zzogl: gcc warning fix

Let's hope variadic macro work on visual

cmake: reenable various warning. With previous fixes it just a matter of a couple of warnings