ada-search-directories

ada-search-directories is a variable defined in `ada-mode.el'.
Its value is

("." "" "/usr/adainclude" "/usr/local/adainclude" "/opt/gnu/adainclude")

Documentation:
Default list of directories to search for Ada files.
See the description for the `ff-search-directories' variable. This variable
is the initial value of `ada-search-directories-internal'.

You can customize this variable.