Within all the introduced static libraries, the module cannot be known
at compilation time. This moves the module name from a compilation
constant to a link time constant string symbol. That way, the same
compiled object within a static library can use a different and correct
module name depending on which plugin it is linked into.

The symbol is hidden so it does not leak between shared objects. For
non-plugins shared libraries (vlccore, vlc, vlc_pulse and
vlc_xcb_events) the module name must be defined manually, unless the
library does not use msg_* macros at all (vlc_vdpau).