[compdb] Expand response files inline based on a switch.
References to response files in a clang compile_commands.json file can
be tricky to deal with when tooling expects all the command flags to be
present in the 'command' field.
This change introduces a '-x' option to '-t compdb' that will expand
@rspfile style response file invocations inline.
E.g.
```sh
$ ninja -t compdb cc
[
{
"directory": "/src/foo",
"command": "cc -foo -bar @foo.obj.rsp",
"file": "foo.cc"
}
]
$ ninja -t compdb -x cc
[
{
"directory": "/src/foo",
"command": "cc -foo -bar foo.cc",
"file": "foo.cc"
}
]
```
1 file changed
