drop irritating warnings about compilation db

[mwhicks1]

Every time you run 3C with a compilation DB, you get this warning:

Error while trying to load a compilation database:
Could not auto-detect compilation database for file "fptrarrstructcallee.c"
No compilation database found in /home/cc/checkedc-clang/clang/test/CheckedCRewriter or any parent directory
fixed-compilation-database: Error while opening fixed database: No such file or directory
json-compilation-database: Error while opening JSON database: No such file or directory
Running without flags.

Can we somehow make it so that these error messages are not shown unless the -verbose flag is on?

[mattmccutchen-cci]

I assume that was supposed to be "without"...

Is there a way we can know whether the user intended to use a compilation DB? If the user did and it doesn't exist, we should report the error.

[mattmccutchen-cci]

There was a little more discussion in Slack.

[mattmccutchen-cci]

After some research, the standard LibTooling answer is: if the user knows they do not want to use a compilation database, they should pass -- at the end of the command line. This will suppress the error and ensure that 3c doesn't detect an unintended compilation database by accident. We can discuss on #343 whether we want to just document this design or change it.

[mattmccutchen-cci]

Duplicate of #343