perf tools: Display better error messages on missing packages

Check for libelf headers and glibc headers separately so that
the error message correctly identifies which package
installation is missing/needed.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: paulus@samba.org
Cc: a.p.zijlstra@chello.nl
Cc: efault@gmx.de
Cc: fweisbec@gmail.com
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <4ADBCCE8.3060300@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>