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='2019-08-26 13:40:46 +0200'>2019-08-26</span></td><td><a href='/guix/commit/gnu/ci.scm?id=f00ff8db9253b077ea625072d41f573cd1f73f3d'>ci: Try hard to build package replacements.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-08-14 21:29:53 +0200'>2019-08-14</span></td><td><a href='/guix/commit/gnu/ci.scm?id=67dac6b8920755cb011047157bb7b4fae4760143'>gnu: mingw: Add x86_64 support.</a><span class='msg-avail'>...</span></td><td>Carl Dong</td></tr>
<tr><td><span title='2019-07-06 16:17:24 +0200'>2019-07-06</span></td><td><a href='/guix/commit/gnu/ci.scm?id=c3ab921eed2a471022e9863a94ea521508782e53'>ci: 'channel-build-system' honors the target system.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-13 23:12:43 +0100'>2019-03-13</span></td><td><a href='/guix/commit/gnu/ci.scm?id=59e80445882f8b0379e54916f89510c0deda6698'>Remove traces of "GuixSD".</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-01-21 10:19:31 +0100'>2019-01-21</span></td><td><a href='/guix/commit/gnu/ci.scm?id=c680a7daa5e143dd37d1d045805e073497c591be'>ci: Skip system tests on armhf-linux.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-01-20 01:42:11 +0100'>2019-01-20</span></td><td><a href='/guix/commit/gnu/ci.scm?id=7e6d8d366a61f951936ed83371877ce006f679f6'>ci: Use a valid 'current-guix'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-01-06 21:41:07 +0100'>2019-01-06</span></td><td><a href='/guix/commit/gnu/ci.scm?id=b5f8c2c88543158e8aca76aa98f9009f6b9e743a'>hydra: Compute jobs in an inferior.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-01-06 21:41:07 +0100'>2019-01-06</span></td><td><a href='/guix/commit/gnu/ci.scm?id=59fb5c1cdb6fa5d6d1dbeca58e33f4a01a7d98f8'>hydra: Move job definitions to (gnu ci).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>