Refactor Makefile.am

- Make headers used as a part of the build process a SOURCE.
- Add missing EXTRA_DIST rules for ilbc/OWNERS.
- Remove obsolete EXTRA_DIST rules.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Fix CMake toolchain

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Update .gitignore

Signed-off-by: Timothy Gu <timothygu99@gmail.com>