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);