Adjust libsanitizer to ABI change in glibc 2.31.

Adapted to 3.x from this upstream commit:
https://github.com/llvm/llvm-project/commit/947f9692440836dcb8d88b74b69dd379d85974ce

--- a/lib/sanitizer_common/saniniitizer_platform_limits_posix.h.orig	2020-08-11 16:01:32.494882282 +0200 #
+++ b/lib/sanitizer_common/sanitizer_platform_limits_posix.h	2020-08-11 16:32:49.711383554 +0200
@@ -176,8 +176,7 @@
     unsigned long __unused1;
     unsigned long __unused2;
 #else
-    unsigned short mode;
-    unsigned short __pad1;
+    unsigned int mode;
     unsigned short __seq;
     unsigned short __pad2;
 #if defined(__x86_64__) && !defined(_LP64)
--- a/lib/sanitizer_common/sanitizer_platform_limits_posix.cc	2020-08-11 16:01:07.926821829 +0200
+++ b/lib/sanitizer_common/sanitizer_platform_limits_posix.cc.orig	2020-08-11 16:01:03.698811421 +0200
@@ -1056,7 +1056,9 @@
 CHECK_SIZE_AND_OFFSET(ipc_perm, gid);
 CHECK_SIZE_AND_OFFSET(ipc_perm, cuid);
 CHECK_SIZE_AND_OFFSET(ipc_perm, cgid);
+#if !SANITIZER_LINUX || __GLIBC_PREREQ (2, 31)
 CHECK_SIZE_AND_OFFSET(ipc_perm, mode);
+#endif
 
 CHECK_TYPE_SIZE(shmid_ds);
 CHECK_SIZE_AND_OFFSET(shmid_ds, shm_perm);
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<tr><td><span title='2020-11-04 11:14:22 +0200'>2020-11-04</span></td><td><a href='/guix/commit/gnu/packages/matrix.scm?id=ecf33bf17c3bf9626612bd5958e2f5a6698c4cfc'>gnu: synapse: Update to 1.22.1.</a><span class='msg-avail'>...</span></td><td>Michael Rohleder</td></tr>
<tr><td><span title='2020-10-15 23:51:04 +0200'>2020-10-15</span></td><td><a href='/guix/commit/gnu/packages/matrix.scm?id=850a2f7417468b8894d17a5659fac83d06fcce41'>gnu: synapse: Update to 1.20.1.</a><span class='msg-avail'>...</span></td><td>Michael Rohleder</td></tr>
115d19db4b639c1e9992'>Use "guile-zlib" and "guile-lzlib" instead of (guix config).</a><span class='msg-avail'>...</span></td><td>Mathieu Othacehe</td></tr>
<tr><td><span title='2020-07-20 23:25:09 +0200'>2020-07-20</span></td><td><a href='/guix/commit/m4?id=e8088f0b06c2193f2cce04a48aa1350229442a9f'>ssh: Speed up RPCs by using #:nodelay.</a><span class='msg-avail'>...</span></td><td>Lars-Dominik Braun</td></tr>
<tr><td><span title='2020-05-28 11:12:40 +0300'>2020-05-28</span></td><td><a href='/guix/commit/m4?id=03e6404936ef0974fdbc877d537b97b28e54124d'>doc: Remove explicit support for mips64el-linux.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2020-05-28 00:55:00 +0200'>2020-05-28</span></td><td><a href='/guix/commit/m4?id=c1dc50ab202fafedde3a6b70ce6339496ad53a51'>maint: Check whether Guile-Gcrypt is recent enough.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-02-22 00:45:58 +0100'>2020-02-22</span></td><td><a href='/guix/commit/m4?id=378918725259d221222dd0b1831fbaa3e0a17e1f'>build: Depend on guile-ssh 0.12.0</a><span class='msg-avail'>...</span></td><td>Lars-Dominik Braun</td></tr>
<tr><td><span title='2019-08-17 19:26:21 +0200'>2019-08-17</span></td><td><a href='/guix/commit/m4?id=611a64bd7e0893057cd04dcdc2a8d5e7ecc39e45'>build: 'GUIX_CHECK_GUILE_JSON' really checks for Guile-JSON 3.x.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-07-25 00:16:41 +0200'>2019-07-25</span></td><td><a href='/guix/commit/m4?id=81c3dc32244a17241d74eea9fa265edfcb326f6d'>maint: Switch to Guile-JSON 3.x.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-05-06 23:21:33 +0200'>2019-05-06</span></td><td><a href='/guix/commit/m4?id=fea338c6ca1922097fa233be85f424c152a4f507'>Add (guix lzlib).</a><span class='msg-avail'>...</span></td><td>Pierre Neidhardt</td></tr>
<tr><td><span title='2018-11-23 15:42:00 +0100'>2018-11-23</span></td><td><a href='/guix/commit/m4?id=60e1c1099fc3d73ed7d3235e71aae5d00ab7d773'>Update Guile-SQLite3 URL everywhere.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-09-04 17:25:11 +0200'>2018-09-04</span></td><td><a href='/guix/commit/m4?id=ca719424455465fca4b872c371daf2a46de88b33'>Switch to Guile-Gcrypt.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-06-01 15:35:15 +0200'>2018-06-01</span></td><td><a href='/guix/commit/m4?id=d59e75f3b5b82692bd250a1a3a9965397bb588c5'>build: Check for Guile-SQLite3.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>