gdb: Update test pattern to deal with native-extended-gdbserver

gdb: Update test pattern to deal with native-extended-gdbserver

When running the test gdb.base/annota1.exp with:

  make check-gdb RUNTESTFLAGS="--target_board=native-extended-gdbserver gdb.base/annota1.exp"

I would see a failure due to some unexpected lines in GDB's output.
The extra lines (when compared with a native run) were about file
transfer from the remote back to GDB.

This commit extends the regexp for this test to allow for these extra
lines, and also splits the rather long regexp up into a list of parts.

With this change in place I see no failures for gdb.base/annota1.exp
when using the native-extended-gdbserver target board, nor with a
native run on X86-64/Linux.

gdb/testsuite/ChangeLog:

	* gdb.base/annota1.exp: Update a test regexp.