kpatch-gcc: fix for .tmp_* objects on RHEL 7

On RHEL 7 I see the following error when trying to patch meminfo.o:

    cp: cannot stat ‘/home/user/.kpatch/obj/fs/proc/.tmp_meminfo.o’: No such file or directory

It turns out that on RHEL 7, a given object foo.o is compiled as
.tmp_foo.o before then being linked as foo.o.  I have no idea why.  The
fix is to record .tmp_foo.o as foo.o in the changed_objs file.