The exec directory for a project is the directory containing the executables for the project's main subprograms.
The exec directory is given by the value of the attribute
in the project file.
for Exec_Dir use "executables";
Exec_Dir has a string value, the path name of the exec
directory. The path name may be absolute or relative to the directory of the
project file. This directory must already exist, and be writable.
By default, when the attribute
Exec_Dir is not given an explicit value
or when its value is the empty string, the exec directory is the same as the
object directory of the project file.