[BusyBox] BB_SRC_DIR broken in 0.49

[Larry Doolittle]

Some of Erik's last-minute changes broke the pristine-source
capability triggered by BB_SRC_DIR in the Makefile.

1. The internal pwd_grp stuff doesn't work with it, but I set
   USE_SYSTEM_PWD_GRP = true, and that bypasses the problems.

2. The new command listed for $(OBJECTS) isn't right.  Simply
   delete the line "       $(CC) $(CFLAGS) -c $*.c -o $*.o" and
   everything will be fine again.

I'm not even sure it's worth fixing these in CVS, since the
to-do list includes a total rearrangement of directory structure.
Please keep pristine-source capability in mind during that reorg.

    - Larry