.gitignore: Add compilation database file and directory

The tool 'bear'[1] can be used to generate the C language server protocol
database file while compiling: 'bear -- make -j $(nproc)'

Add the database file into .gitignore as Linux Kernel [2] does.

The clangd will parse the compile_commands.json language metadata into the
.cache directory. Add it for clean git status track.

[1]: https://github.com/rizsotto/Bear
[2]: https://git.kernel.org/torvalds/c/26c4c71bcd9a

Signed-off-by: Haiyue Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

.gitignore

@@ -33,6 +33,10 @@
 /test/*.dmesg
 /test/output/
 
+# Clang's compilation database file and directory.
+/.cache
+/compile_commands.json
+
 config-host.h
 config-host.mak
 config.log