copy over some things from the macgdb git submodule

also:
- run testsuite
- gitignore more things
- add `--enable-64-bit-bfd` configure flag to configure script in src/
- let dejagnu be configured from the configure script in src/
- fix exeext being set for expect on platforms where it is NOT needed
(this allows expect-based testsuites to be run with this local copy of
expect)
- more comments in the configure script in src/expect/testsuite
- more configure checks in src/gdb/
- various other tweaks

Change-Id: I5f013e8f0aa1e1e4f77cdbc66b6bd3c814d6a1da