Makefile: Fix "make cscope TAGS"

Cscope and TAGS files work in source directory rather than the build
directory, also, don't ask users to run configure first, because they
may have an out of tree build.

Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>