The dynamic-list-file used to export dynamic symbols introduced in

commit e3d09ec8 ("tools lib traceevent: Export dynamic symbols
used by traceevent plugins")

is generated without any sort of error checking.

I experienced problems due to an old version of nm (v 0.158) that outputs
in a format distinct from the assumed by the script.

Robustify the built of dynamic symbol list  by enforcing that the second
column of $(NM) -u <files> is either "U" (Undefined), "W" or "w" (undefined
weak), which are the possible outputs from non-ancient $(NM) versions.
Print an error if format is unexpected.

v2: Accept "W" and "w" symbol options.
Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michal Marek <mmarek@suse.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/20170208052840.112182-1-davidcc@google.com
[ Use STRING1 = STRING1 instead of == to make this work on Ubuntu systems ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>