algol68: Fix SPARC build

algol68: Fix SPARC build

Algol68 bootstrap currently fails on Solaris/SPARC:

n file included from ./tm_p.h:4,
                 from gcc/algol68/a68-imports.cc:36:
gcc/config/sparc/sparc-protos.h:46:47: error: use of enum ‘memmodel’ without previous declaration
   46 | extern void sparc_emit_membar_for_model (enum memmodel, int, int);
      |                                               ^~~~~~~~

tm_p.h needs memmodel.h on some targets, like SPARC.

Bootstrapped on sparc-sun-solaris2.11.

2025-12-01  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>

	gcc/algol68:
	* a68-exports.cc: Include memmodel.h.
	* a68-imports.cc: Likeswise.