soundlib in the Makefile hints updated

Move pieces of the Makefile hints sound-related changes that
are not macOS-specific from sys/unix/hints/macOS.370 to some new
include files. The WANT_MACSOUND block stays in
sys/unix/hints/macOS.370 because it is system-specific.

Before this change, the various Makefiles were assembled via
hints files macOS.370 or linux.370. Both were using included
portions from the following files in the sys/unix/hints/include
directory, in this sequence:

    -INCLUDE multiw-1.370
    -INCLUDE multiw-2.370
    -INCLUDE compiler.370
    -INCLUDE multiw-3.370
    -INCLUDE cross-pre.370
    -INCLUDE gbdates-pre.370
    -INCLUDE gbdates-post.370
    -INCLUDE cross-post.370

After this change, the various Makefiles will still be assembled
via hints files macOS.370 or linux.370. They will continue to use
included portions from the following files in the
sys/unix/hints/include directory, but with three additional
include files related to sound and soundlibs. This is the new
sequence:

    -INCLUDE multiw-1.370
    -INCLUDE multiw-2.370
    -INCLUDE compiler.370
    -INCLUDE multiw-3.370
+   -INCLUDE multisnd1-pre.370
    -INCLUDE cross-pre.370
    -INCLUDE gbdates-pre.370
+   -INCLUDE multisnd2-pre.370
    -INCLUDE gbdates-post.370
+   -INCLUDE multisnd-post.370
    -INCLUDE cross-post.370

The include mechanism continues to allow common portions that can
be shared between macOS and Linux to be maintained in a single
place only, with minimal duplication. Now, that has been extended
to include Makefile lines related to sounds and soundlib.

sys/unix/hints/linux.370

@@ -113,18 +113,20 @@ endif   #MAKEFILE_SRC
 endif   #HAVE_NCURSESW
 endif   #WANT_WIN_CURSES
 
-# HAVE_SNDLIB could have been set in multiw-2 for Qt.
-# If it is set, add USER_SOUNDS
-ifeq "$(HAVE_SNDLIB)" "1"
-SNDCFLAGS+= -DUSER_SOUNDS
-endif
+#
+#-INCLUDE multisnd1-pre.370
+#
 
-CFLAGS+= $(WINCFLAGS)	  #WINCFLAGS set from multiw-2.370
-CFLAGS+= $(SNDCFLAGS)     #SNDCFLAGS set from multiw-2.370
+# WINCFLAGS set from multiw-2.370
+# SNDCFLAGS set from multisnd-pre.370
+CFLAGS+= $(WINCFLAGS)
+CFLAGS+= $(SNDCFLAGS)
 CFLAGS+= $(NHCFLAGS)
 
-CCXXFLAGS+= $(WINCFLAGS)  #WINCFLAGS set from multiw-2.370
-CCXXFLAGS+= $(SNDCFLAGS)   #SNDCFLAGS set from multiw-2.370
+# WINCFLAGS set from multiw-2.370
+# SNDCFLAGS set from multisnd-pre.370
+CCXXFLAGS+= $(WINCFLAGS)
+CCXXFLAGS+= $(SNDCFLAGS)
 CCXXFLAGS+= $(NHCFLAGS)
 
 VARDATND =
@@ -313,15 +315,19 @@ GAMEPERM = 0755
 #-INCLUDE gbdates-pre.370
 #
 
+#
+#-INCLUDE multisnd2-pre.370
+#
+
 #-POST
 
 #
 #-INCLUDE gbdates-post.370
 #
+#
+#-INCLUDE multisnd-post.370
+#
 
-#
-#-INCLUDE cross-post.370
-#
 ifdef WANT_LIBNH
 $(TARGETPFX)libnh.a: $(HOBJ) $(LIBNHSYSOBJ) ../lib/lua/liblua.a
 	$(AR) rcs $@ $(HOBJ) $(LIBNHSYSOBJ) ../lib/lua/liblua.a
@@ -331,4 +337,8 @@ $(TARGETPFX)libnhmain.o : ../sys/libnh/libnhmain.c $(HACK_H)
 $(TARGETPFX)winshim.o : ../win/shim/winshim.c $(HACK_H)
 	$(CC) $(CFLAGS) -c -o$@ $<
 endif  # WANT_LIBNH
+
 #
+#-INCLUDE cross-post.370
+#
+