In order to link dynamically with the library you do:

gprbuild -v -aI/usr/include/strings-edit\
         -aO/usr/lib[64]/strings-edit\
          APPLICATION\
         -largs -lstrings-edit\

To link statically:

gprbuild -v -aI/usr/include/strings-edit\
         -aO/usr/lib[64]/strings-edit\
          APPLICATION\
         -largs /usr/lib[64]/libstrings-edit.a\

You  can  also  use the gpr file in your project files. The project file
uses the external variable Library_Type to control linkage. It can  take
values "relocatable" (default) or "static". For example:

   with strings_edit.gpr";
   project My_Project is
      for Main use ("My_Progran");
   end My_Project;

which can be built (dynamically linking to the library) as:

gprbuild -v -Pmy_project.gpr

or statically:

gprbuild -v -XLibrary_Type=static -Pmy_project.gpr

See also:
   /usr/lib/gnat - strings_edit.gpr
   /usr/include/strings-edit - *.adb, *.ads
   /usr/lib[64] - libstrings-edit.so.3.11-1
   /usr/lib[64]/strings-edit - *.ali, libstrings-edit.a
   /usr/share/strings-edit - *.htm documentation, tests and examples
