Make sure the creation of option_table.c and option_table.o happens
atomically.

Signed-off-by: Stefan Reinauer <stepan@coresystems.de>

Index: src/config/Config.lb
===================================================================
--- src/config/Config.lb	(revision 3782)
+++ src/config/Config.lb	(working copy)
@@ -181,9 +181,15 @@
 	action	"$(HOSTCC) $(HOSTCFLAGS) $(CPUFLAGS) $< -o $@" 
 end
 
+# make seems to assume that a non-phony dependency is satisfied if the target
+# file exists, not if the according rule has been completely finished.  The
+# following rule makes sure we don't confuse make with partly created or empty
+# option_table.[ch] files in case coreboot is compiled with make -j.
 makerule option_table.h option_table.c
 	depends	"build_opt_tbl $(MAINBOARD)/cmos.layout" 
-	action	"./build_opt_tbl -b  --config $(MAINBOARD)/cmos.layout --header option_table.h --option option_table.c"
+	action	"./build_opt_tbl -b  --config $(MAINBOARD)/cmos.layout --header option_table.h.tmp --option option_table.c.tmp"
+	action  "mv option_table.c.tmp option_table.c"
+	action  "mv option_table.h.tmp option_table.h"
 end
 
 if HAVE_OPTION_TABLE
