[gdb] Use using instead of typedef

After commit 1eed06ae51d ("[gdbsupport] Use using instead of typedef in
next_iterator") I wondered if I could do something similar using sed.

Result of:
...
$ find gdb* -type f -name "*.[ch]" -o -name "*.cc" \
    | egrep -v /testsuite/ \
    | xargs sed -i \
	    's/^\([ \t]*\)typedef \([a-zA-Z_0-9:<>,.() ]*\) \([\*&][\*&]*\)\([a-zA-Z_0-9]*\);/\1using \4 = \2 \3;/'

$ find gdb* -type f -name "*.[ch]" -o -name "*.cc" \
    | egrep -v /testsuite/ \
    | xargs sed -i \
	    's/^\([ \t]*\)typedef \([a-zA-Z_0-9:<>,.() ]*\) \([a-zA-Z_0-9]*\);/\1using \3 = \2;/'
...

Tested on x86_64-linux.