btrfs-progs: build: do not regenerate kernel-lib/tables.c

As reported in
https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg66765.html
cross-compilation does not work very well with current tables.c. We can
simpy keep the pergenerated file in the repository and update if needed.

Signed-off-by: David Sterba <dsterba@suse.com>

Makefile

@@ -325,7 +325,9 @@ mktables: kernel-lib/mktables.c
 	@echo "    [CC]     $@"
 	$(Q)$(CC) $(CFLAGS) $< -o $@
 
-kernel-lib/tables.c: mktables
+# the target can be regenerated manually using mktables, but a local copy is
+# kept so the build process is simpler
+kernel-lib/tables.c:
 	@echo "    [TABLE]  $@"
 	$(Q)./mktables > $@ || ($(RM) -f $@ && exit 1)
 
@@ -518,7 +520,6 @@ clean: $(CLEANDIRS)
 	$(Q)$(RM) -f -- $(progs) *.o *.o.d \
 		kernel-lib/*.o kernel-lib/*.o.d \
 		kernel-shared/*.o kernel-shared/*.o.d \
-		kernel-lib/tables.c \
 		image/*.o image/*.o.d \
 		convert/*.o convert/*.o.d \
 		mkfs/*.o mkfs/*.o.d \