Attribiutes GH PR #647: https://github.com/ArcticaProject/nx-libs/pull/647

Attributes GH PR #646: https://github.com/ArcticaProject/nx-libs/pull/646

Attributes GH PR #645: https://github.com/ArcticaProject/nx-libs/pull/645

Attributes GH PR #658: https://github.com/ArcticaProject/nx-libs/pull/658

Fixes: ArcticaProject/nx-libs#657

Fixes ArcticaProject/nx-libs#657.

Attributes GH PR #644: https://github.com/ArcticaProject/nx-libs/pull/644

According to the C standard these are not equivalent. However, the
same change has been done in Xorg upstream. Plus these functions are
not called with parameters anywhere so we should be fine.

Besides, include/{extinit.h,XIstubs.h} always had the "void".

Was forgotten in f6a1bda2

Attributes GH PR #663: https://github.com/ArcticaProject/nx-libs/pull/663

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

Fixes: ArcticaProject/nx-libs#661

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

m4/nx-macros.m4: add NX_TARGET_USE_ELF macro, setting TARGET_ELF automake conditional if target compiler is generating ELF binaries.

This reverts commit c804d99f.

It seems like the missing code was missing for a good reason. Including
it leads to very strange issues when coupled with libXcomp and using
connection speed settings lower than LAN (and even on LAN some icons
are not showing up correctly, e.g., when using MATE).

Further investigation on why this happens pending and might happen at a
later time.

Fixes: ArcticaProject/nx-libs#656

On PPC64*, X_BYTE_ORDER was hardcoded to X_BIG_ENDIAN. Since the CPUs
support both modes and we actually intend to execute nxagent on ppc64le
as well, detect the actual endianess and add support for
Ppc64LeArchitecture.