Makefile: bugfix for parallel builds

When using "make -j" we must make silentoldconfig before building
any object. Otherwise we may use the previous autoconf.h, in error
if we just changed the configuration.

This was exposed by ./MAKEALL with the properly working wr/non-wr build
for wrs: previous wrcp_defconfig left CONFIG_EXT_WR active while
building some file with wrs-nonwr_defconfig.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>

Makefile

@@ -87,11 +87,11 @@ export CFLAGS
 # The object only depends on OBJ-y because each subdirs added needed
 # libraries: see proto-standard/Makefile as an example.
 
-$(TARGET).o: silentoldconfig $(OBJ-y)
+$(TARGET).o: $(OBJ-y)
 	$(LD) -Map $(TARGET).map1 -r -o $@ $(PPSI_O_LDFLAGS) \
 		--start-group $(OBJ-y) --end-group
 
-$(OBJ-y): $(wildcard include/ppsi/*.h)
+$(OBJ-y): silentoldconfig $(wildcard include/ppsi/*.h)
 
 # Finally, "make clean" is expected to work
 clean: