Clean up what `make install` does (e.g. no systemd/SMF on win32 builds)

[jimklimov]

Notably, check also if these files and configure options are not shoved down on users of all other non-linux/non-solarish platforms.

[jimklimov]

Clumsy hot-fixes applied to scripts/Windows/build-mingw-nut.sh to require lack of systemd files with Windows cross-builds (probably become enabled when the build host is Linux and its systemd support is detected via hardcoded paths).

Even clumsier hotfix is for scripts/Solaris/Makefile.am to only install solaris-init content if packaging for Solaris, or if SMF support got enabled.