mkdir error message from bash function setup_dirs

[RobertHenry6bev]

Initial cost estimate: 2 days
Initial contacts: @safern, @trylek

Running on ubuntu 19.10.

The 2nd of 3 invocation of the function setup_dirs from file eng/native/build-commons.sh is being called with $__IntermediatesDir either unset or set to the empty string. The result is a call
mkdir -p ""
which results in this error message:

mkdir: cannot create directory ‘’: No such file or directory

Please aggressively use the shell flags -u (fail on undefined variable) and -e (fail on subcommand fail) to find errors like this.

I invoke the build thusly:
bash ./build.sh -subsetCategory coreclr --configuration Debug --clang9

[ghost]

Area Owners

@jeffschwMSFT, @jashook, @trylek

[danmoseley]

Thanks @RobertHenry6bev . Do you have any interest in offering a PR?