You need the crate in order to use the dependency through Alire, but if you just simply want to use the library, after installation in Debian, the project file will be directly visible to be used by gprbuild (at least if this program also comes from Debian).
That is, in ttcheck.gpr:
with "texttools";
project ttcheck is
-- Whatever else you need
end ttcheck;
Nevertheless, having this library as an Alire crate would be good news. In fact, all the Ada libraries already on Debian should be on the Alire index too.