gyp: move compile_commands_json

It isn't possible to access
`tools/gyp/pylib/gyp/generator/compile_commands_json.py` using the
`--format` option.

This commit moves the file in a place where it can be accessed.

Fixes: #1526
PR-URL: #1661
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Signed-off-by: Paul Maréchal <paul.marechal@ericsson.com>

Author: paul-marechal