One cannot simply pass down a va_list to another function that expects
variable arguments ("..."). The prototype of the called functions must
expect a va_list argument instead.

This fixes segfaults that happen e.g. after compiling X11.cpp with
TEST and effectively reverts 59e829f3.

Instead of using a pragma which will be valid for the whole file this
only affects the functions where it is actually required and supresses
"format string is not a string literal" warnings.

According to GCC documentation the second attribute parameter should
be 0:

"For functions where the arguments are not available to be checked
(such as vprintf), specify the third parameter as zero".

Found via Travis CI

nxcompshad/{configure.ac,src/Makefile.am}: only enable new ELF dtags if target system actually is ELF-based.

Same method as used in the previous commit, but easier done thanks to
autotools and libtool.

Fixes: ArcticaProject/nx-libs#610

Fixes ArcticaProject/nx-libs#572

 This code can be reactivated any time in the future once
 some potential maintainer turns up and makes this work
 on the MS Windows / Cygwin platform.

nxcompshad: Rewrite Logger class methods to properly take advantage of the 'gnu_printf' format attribute.

nxcompshad/src/Shadow.cpp: Drop duplicate prototype for NXShadowRemoveAllUpdaters(). Already in Shadow.h.

nxcompshad/src/Regions.h: Avoid warning: ‘typedef’ was ignored in this declaration. Drop typedef declaration from _XRegion struct.