Update .gitignore files

* Ignore build-debug (this is a common sub-directory for debug builds).
* Ignore .cache (this is a clangd LSP directory
* Ignore compile_commands (can be generated by CMake used by LSP
  clients)
* Update copyright date.

Signed-off-by: Jack Frankland <jack.frankland@arm.com>
Change-Id: I74a5bc8c03f51e2d534d4870b58d477e830f6f42