perf symbols: perf_header__read_build_ids() offset'n'size should be u64

As off_t is a long, so breaking things on 32-bit land. Now
buildids work on 32-bit land.

[root@ana ~]# uname -a
Linux ana.ghostprotocols.net 2.6.31.6-162.fc12.i686 #1 SMP Fri
Dec 4 01:09:09 EST 2009 i686 i686 i386 GNU/Linux [root@ana ~]#
perf buildid-list | tail -5
136ee6792ba2ae57870ecd87369f4ae3194d5b27 /lib/libreadline.so.6.0
d202dcb1ad48d140065783657d37ae3f2d9ab83f /usr/bin/gdb
0a56c0c00dcc2e9e581ae9997f31957c9c4671df
/usr/lib/libdwarf.so.0.0
5f9e6ac95241cbb3227608e0ff2a2e0cbbe72439 /home/acme/bin/perf
925d19eccc2ddb1c9d74dd178a011426f1b124a8 /bin/sleep [root@ana ~]#

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <1260396578-19116-2-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>