SQLite3 defaults to 0644 unless overridden, relying on the process'
umask to make that tighter.
Our in-tree SQLite3 uses 0600 as the permissions for DB files it
creates.
Out-of-tree builds of SQLite3 probably get the 0644 default.
We can't change the umask in libraries -- it's not thread-safe.
So this commit changes the SCC ccache type's default ccname to include
an intermediate directory which is created with `mkdir(2)` with
permissions set to 0700, then it chmods the DB file to 0644.
6f7c6a7f67