Adds a new conditional parsing variable used to evaluation conditional statements such as #if while parsing code.
Hprj is a handle to the project. If hprj is hNil, then the new variable is added to the global condition list.
The name of the variable is given in szName, and the value is given in szValue
There are two condition lists: the global list and the project-specific list. When you open a project, the two lists are merged, with the project-specific list taking precedence over entries in the global list.