Alan. I never used srcpath before and after some trial and error I feel that
the source of the problem is bad description of the option in JDK.
Ant passes srcpath directly to JDK's javac (unlike srcdir which Ant itself
searches for java files).
The description says "Specify" or "Specifies", but
This actually does what I want:
The problem is that I don’t really want to specify srcdir, but if I leave it
out, the build fails (see below).
I would need to create a fake directory to use as srcdir to be sure that I
don’t accidentally compile unwanted source
