Merge tag 'kvm-x86-selftests_utils-6.10' of https://github.com/kvm-x86/linux into HEAD

KVM selftests treewide updates for 6.10:

 - Define _GNU_SOURCE for all selftests to fix a warning that was introduced by
   a change to kselftest_harness.h late in the 6.9 cycle, and because forcing
   every test to #define _GNU_SOURCE is painful.

 - Provide a global psuedo-RNG instance for all tests, so that library code can
   generate random, but determinstic numbers.

 - Use the global pRNG to randomly force emulation of select writes from guest
   code on x86, e.g. to help validate KVM's emulation of locked accesses.

 - Rename kvm_util_base.h back to kvm_util.h, as the weird layer of indirection
   was added purely to avoid manually #including ucall_common.h in a handful of
   locations.

 - Allocate and initialize x86's GDT, IDT, TSS, segments, and default exception
   handlers at VM creation, instead of forcing tests to manually trigger the
   related setup.

tools/testing/selftests/kvm/rseq_test.c

@@ -1,5 +1,13 @@
 // SPDX-License-Identifier: GPL-2.0-only
-#define _GNU_SOURCE /* for program_invocation_short_name */
+
+/*
+ * Include rseq.c without _GNU_SOURCE defined, before including any headers, so
+ * that rseq.c is compiled with its configuration, not KVM selftests' config.
+ */
+#undef _GNU_SOURCE
+#include "../rseq/rseq.c"
+#define _GNU_SOURCE
+
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
@@ -19,8 +27,7 @@
 #include "kvm_util.h"
 #include "processor.h"
 #include "test_util.h"
-
-#include "../rseq/rseq.c"
+#include "ucall_common.h"
 
 /*
  * Any bug related to task migration is likely to be timing-dependent; perform