Added dependency rules for Objects/stringlib/*.h

stringobject, unicodeobject and the two formatters are rebuild whenever a header files changes

Makefile.pre.in

@@ -517,27 +517,27 @@ Python/importdl.o: $(srcdir)/Python/importdl.c
 Objects/unicodectype.o:	$(srcdir)/Objects/unicodectype.c \
 				$(srcdir)/Objects/unicodetype_db.h
 
-Objects/unicodeobject.o: $(srcdir)/Objects/unicodeobject.c \
-				$(srcdir)/Objects/stringlib/string_format.h \
-	                        $(srcdir)/Objects/stringlib/unicodedefs.h \
-	                        $(srcdir)/Objects/stringlib/fastsearch.h \
+STRINGLIB_HEADERS= \
 		$(srcdir)/Objects/stringlib/count.h \
+		$(srcdir)/Objects/stringlib/fastsearch.h \
 		$(srcdir)/Objects/stringlib/find.h \
-	                        $(srcdir)/Objects/stringlib/partition.h
+		$(srcdir)/Objects/stringlib/formatter.h \
+		$(srcdir)/Objects/stringlib/partition.h \
+		$(srcdir)/Objects/stringlib/stringdefs.h \
+		$(srcdir)/Objects/stringlib/string_format.h \
+		$(srcdir)/Objects/stringlib/unicodedefs.h
+
+Objects/unicodeobject.o: $(srcdir)/Objects/unicodeobject.c \
+				$(STRINGLIB_HEADERS)
 
 Objects/stringobject.o: $(srcdir)/Objects/stringobject.c \
-				$(srcdir)/Objects/stringlib/string_format.h \
-	                        $(srcdir)/Objects/stringlib/stringdefs.h \
-	                        $(srcdir)/Objects/stringlib/fastsearch.h \
-	                        $(srcdir)/Objects/stringlib/count.h \
-	                        $(srcdir)/Objects/stringlib/find.h \
-	                        $(srcdir)/Objects/stringlib/partition.h
+				$(STRINGLIB_HEADERS)
 
 Python/formatter_unicode.o: $(srcdir)/Python/formatter_unicode.c \
-	                        $(srcdir)/Objects/stringlib/formatter.h
+				$(STRINGLIB_HEADERS)
 
 Python/formatter_string.o: $(srcdir)/Python/formatter_string.c \
-	                        $(srcdir)/Objects/stringlib/formatter.h
+				$(STRINGLIB_HEADERS)
 
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 # Header files