x86: disable image size check for test builds

64-bit allyesconfig builds fail with

x86_64-linux-ld: kernel image bigger than KERNEL_IMAGE_SIZE

Bisect points to commit 6f110a5 ("Disable SLUB_TINY for build
testing") as the responsible commit.  Reverting that patch does indeed fix
the problem.  Further analysis shows that disabling SLUB_TINY enables
KASAN, and that KASAN is responsible for the image size increase.

Solve the build problem by disabling the image size check for test
builds.

[akpm@linux-foundation.org: add comment, fix nearby typo (sink->sync)]
[akpm@linux-foundation.org: fix comment snafu
  Link: https://lore.kernel.org/oe-kbuild-all/202504191813.4r9H6Glt-lkp@intel.com/
Link: https://lkml.kernel.org/r/20250417010950.2203847-1-linux@roeck-us.net
Fixes: 6f110a5 ("Disable SLUB_TINY for build testing")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Borislav Betkov <bp@alien8.de>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: <x86@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: groeck

arch/x86/kernel/vmlinux.lds.S

@@ -466,10 +466,18 @@ SECTIONS
 }
 
 /*
- * The ASSERT() sink to . is intentional, for binutils 2.14 compatibility:
+ * COMPILE_TEST kernels can be large - CONFIG_KASAN, for example, can cause
+ * this.  Let's assume that nobody will be running a COMPILE_TEST kernel and
+ * let's assert that fuller build coverage is more valuable than being able to
+ * run a COMPILE_TEST kernel.
+ */
+#ifndef CONFIG_COMPILE_TEST
+/*
+ * The ASSERT() sync to . is intentional, for binutils 2.14 compatibility:
  */
 . = ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
 	   "kernel image bigger than KERNEL_IMAGE_SIZE");
+#endif
 
 /* needed for Clang - see arch/x86/entry/entry.S */
 PROVIDE(__ref_stack_chk_guard = __stack_chk_guard);