See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86724
Author: Rainer Jung
Date: 2018-07-29

isl 0.20 stopped including other unused header files in their header files.
Therefore,now it's necessary to include the stuff ourselves.
--- .../gcc/graphite.h 2018-01-03 11:03:58.000000000 +0000
+++ .../gcc/graphite.h 2018-07-29 17:42:55.836121000 +0000
@@ -37,6 +37,8 @@
 #include <isl/schedule.h>
 #include <isl/ast_build.h>
 #include <isl/schedule_node.h>
+#include <isl/id.h>
+#include <isl/space.h>

 typedef struct poly_dr *poly_dr_p;
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<tr><td><span title='2020-04-16 23:41:52 +0200'>2020-04-16</span></td><td><a href='/guix/commit/doc/package-hello.json?id=c9f321e52a99dea93fcc099372ea0167150b9aac'>doc: Document building and installing from JSON files.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Invoking guix package): Augment pargraphs for
"--install-from-file".
(Invoking guix build): Document building from JSON files.
* doc/package-hello.json: New file.
* doc/local.mk (EXTRA_DIST): Add it.
</span></span></td><td>Ricardo Wurmus</td></tr>