[gdb/contrib] Combine sed invocations in words.sh script

[gdb/contrib] Combine sed invocations in words.sh script

Currently running words.sh on all the c source and header files in the repo
takes ~16s in user time:
...
$ time ./gdb/contrib/words.sh \
    $(find -type f -name "*.c" -o -name "*.h") \
    >/dev/null

real    0m7,787s
user    0m16,349s
sys     0m0,367s
...

Rewrite the sed invocations using the -e option from this:
...
   | sed <sedprog1>
   | sed <sedprog2>
...
into this:
...
   | sed \
       -e <sedprog1>
       -e <sedprog2>
...
and reduce user time to ~11s:
...
$ time ./gdb/contrib/words.sh \
    $(find -type f -name "*.c" -o -name "*.h") \
    >/dev/null

real    0m7,243s
user    0m11,220s
sys     0m0,205s
...

gdb/ChangeLog:

2019-11-22  Tom de Vries  <tdevries@suse.de>

	* contrib/words.sh: Combine sed invocations.

Change-Id: Ib08453f3712f32ed02d9f503ee960711ebb9421b