perf tools: Fix linking errors with --as-needed flag

perf tools: Fix linking errors with --as-needed flag

External shared libraries should never be appended to the LDFLAGS as this
messes the linking order. As EXTLIBS collects those libraries, it seems that
perl and python libraries  should also be appended to EXTLIBS.

Also fix the broken linking order.

This is a refresh of a patch by Ozan Çağlayan and improved by both Tom Zanussi
and Kirill A. Shutemov.

Cc: Ozan Çağlayan <ozan@pardus.org.tr>
Tested-by: Kirill A. Shutemov <kirill@shutemov.name>
Tested-by: Tom Zanussi <tzanussi@gmail.com>
LKML-Reference: <1282627430.28324.8.camel@tropicana>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>