Add another auto-generated file to .gitignore.

* Update tools/kconfig/.gitignore for auto-generated file *.o.

Merges https://github.com/espressif/esp-idf/pull/3073

tools/kconfig/.gitignore

@@ -11,6 +11,7 @@ zconf.hash.c
 gconf.glade.h
 *.pot
 *.mo
+*.o
 
 #
 # configuration programs