This patch adds a bunch of generated files to gdb's gitignore files.
There are still a bunch of "stamp" files that are not ignored, but I
think the rule for them should be put in the top-level gitignore.
Users and developers are encouraged to build out-of-tree, but some
people prefer the simplicity to build in-tree, so it should be useful
for them.
gdb/ChangeLog:
* .gitignore: Ignore more files.
* data-directory/.gitignore: Likewise.