Makefile: limit make re-execution to avoid infinite spin

make-4.4 became intentionally more eager at rebuilding outdated Makefile
includes. Currently this causes `dtc` to spin infinitely in
parser/dependency loop:

    $ make
    ...
        CHK version_gen.h
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
        CHK version_gen.h
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
    ... # never stops

After the change build eventually fails when gets into this state:

    $ make
    ...
        CHK version_gen.h
        UPD version_gen.h
         DEP util.c
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
        CHK version_gen.h
         BISON dtc-parser.tab.h
         DEP dtc-lexer.lex.c
         DEP dtc-parser.tab.c
    Makefile:394: *** "Make re-executed itself 10 times. Infinite recursion?".  Stop.

The actual recursion will be fixed separately.

Signed-off-by: Sergei Trofimovich <slyich@gmail.com>

Makefile

@@ -389,3 +389,7 @@ clean: libfdt_clean pylibfdt_clean tests_clean
 	$(BISON) -b $(basename $(basename $@)) -d $<
 
 FORCE:
+
+ifeq ($(MAKE_RESTARTS),10)
+$(error "Make re-executed itself $(MAKE_RESTARTS) times. Infinite recursion?")
+endif