Unbreak build on BSDs and Solaris after relative saves

[jbeich]

Regressed by e5138a9. From error log:

c++ -O2 -pipe -fstack-protector-strong -fno-strict-aliasing   -c  -DUSE_X86_GFX -O2 -pipe -fstack-protector-strong -fno-strict-aliasing   -I/usr/local/include/SDL2 -I/usr/local/include -D_REENTRANT -D_THREAD_SAFE -I/usr/local/include -I/usr/local/include/smpeg2 -I/usr/local/include/SDL2 -I/usr/local/include -D_REENTRANT -D_THREAD_SAFE -I/usr/local/include/freetype2 -I/usr/local/include/libpng16  -DLINUX -DUSE_OGG_VORBIS -DCONST_ICONV  -DENABLE_JOYSTICK PonscripterLabel.cpp
PonscripterLabel.cpp:68:10: fatal error: 'linux/limits.h' file not found
#include <linux/limits.h>
         ^~~~~~~~~~~~~~~~
1 error generated.
gmake[2]: *** [Makefile.ponscripter:61: PonscripterLabel.o] Error 1

-DLINUX is passed on FreeBSD, NetBSD, OpenBSD, Solaris, not just Linux.

ponscripter-fork/configure

Lines 294 to 298 in 4f887b8

	*linux*) echo "Linux"; POSIX=Linux ;;
	*solaris*) echo "Solaris"; POSIX=Solaris ;;
	*freebsd*) echo "FreeBSD"; POSIX=FreeBSD ;;
	*netbsd*) echo "NetBSD"; POSIX=NetBSD ;;
	*openbsd*) echo "OpenBSD"; POSIX=OpenBSD ;;

ponscripter-fork/configure

Lines 986 to 1015 in 4f887b8

	Posix)
	case "$POSIX" in
	Linux) INTERNAL_LDFLAGS="-ldl -lasound" ;;
	FreeBSD) INTERNAL_LDFLAGS="-L/usr/X11R6/lib -lX11 -lXi -lXrandr -liconv"
	EXTRA_DEPS="-DCONST_ICONV" ;;
	NetBSD) INTERNAL_LDFLAGS="\$(foreach x,11 i randr ext render,/usr/X11R6/lib/libX\$(x).a) -lossaudio" ;;
	OpenBSD) INTERNAL_LDFLAGS="-L/usr/X11R6/lib -lX11 -lXi -lXrandr -lossaudio" ;;
	Solaris) INTERNAL_LDFLAGS="-lX11 -lXext"
	# Thanks for the unnecessary and incompatible iconv library, GNU.
	if $INTERNAL_SDL && test -f /usr/local/include/iconv.h; then
	INTERNAL_LDFLAGS="$INTERNAL_LDFLAGS -L/usr/local/lib -liconv"
	fi
	EXTRA_DEPS="-DCONST_ICONV"
	# Stripping binaries can break them, so we don't.
	STRIPFLAG=
	;;
	esac
	cat >> $MAKEFILE <<_EOF
	LIBS = $OURLIBS \\
	$LINKSDL2_image \$(if \$(findstring true,$INTERNAL_SDL_IMAGE),$LINKjpeg $LINKpng $LINKz) \\
	$LINKSDL2_mixer \$(if \$(findstring true,$INTERNAL_SDL_MIXER$EXPLICIT_OGGLIBS),$LINKvorbisfile $LINKvorbis $LINKogg) \\
	\$(shell \$(SHELLENV) $SDL_CONFIG --libs) \\
	\$(shell \$(SHELLENV) $SMPEG_CONFIG --libs) \\
	\$(shell \$(SHELLENV) $FREETYPE_CONFIG --libs) \\
	$LINKbz2 \$(if \$(findstring true,$INTERNAL_SDL),$INTERNAL_LDFLAGS)
	DEFS = -DLINUX -DUSE_OGG_VORBIS $EXTRA_DEPS $OURDEFS
	EXT_OBJS = $GFX_EXT_OBJS
	_EOF