isl-0.26 moves some header includes around so now if we want
isl_val_free we need to include isl/val.h. Otherwise we get errors such
as
src/gcc/gcc/graphite-isl-ast-to-gimple.c: In member function 'tree_node* translate_isl_ast_to_gimple::gcc_expression_from_isl_expr_int(tree, isl_ast_expr*)':
src/gcc/gcc/graphite-isl-ast-to-gimple.c:349:3: error: 'isl_val_free' was not declared in this scope; did you mean 'isl_vec_free'?
349 | isl_val_free (val);
| ^~~~~~~~~~~~
| isl_vec_free
Bring in an upstream fix that uses the correct header file.
Fixes#1962
Signed-off-by: Chris Packham <judge.packham@gmail.com>