Fix libdwarf include path to fit debian-like systems too.

Borislav Petkov reported:

> even after installing libdwarf-dev on my debian box here,
> make in tools/perf/ still complains that it cannot find libdwarf:
>
> Makefile:491: No libdwarf.h found or old libdwarf.h found, disables dwarf
> support. Please install libdwarf-dev/libdwarf-devel >= 20081231
>
> The problem is that the include path on debian is not
> /usr/include/libdwarf/ but simply /usr/include because the debian
> package libdwarf-dev puts the headers straight into
> /usr/include.

This patch adds -I/usr/include/libdwarf to BASIC_CFLAGS
and fix probe-finder.h to include just libdwarf.h/dwarf.h.

This patch also adds a workaround for the undefined _MIPS_SZLONG
bug in libdwarf.h.
Reported-by: Borislav Petkov <borislav.petkov@amd.com>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Gabor Gombas <gombasg@sztaki.hu>
Cc: systemtap <systemtap@sources.redhat.com>
Cc: DLE <dle-develop@lists.sourceforge.net>
LKML-Reference: <20091216221618.13816.83296.stgit@dhcp-100-2-132.bos.redhat.com>
[ v2: small stylistic fixlets to probe-finder.h ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>