When LTO is used, some ___ksymtab_string sections are seen by this sed
script, creating lines containing a single ) such as:

EXPORT(foo)
)
)
EXPORT(bar)

Let's make it so the + character is also required for any line to be
printed.
Signed-off-by: NNicolas Pitre <nico@linaro.org>
Signed-off-by: NMichal Marek <mmarek@suse.com>