mm: make arch_has_descending_max_zone_pfns() static

clang produces a build failure on x86 for some randconfig builds after a
change that moves around code to mm/mm_init.c:

Cannot find symbol for section 2: .text.
mm/mm_init.o: failed

I have not been able to figure out why this happens, but the __weak
annotation on arch_has_descending_max_zone_pfns() is the trigger here.

Removing the weak function in favor of an open-coded Kconfig option check
avoids the problem and becomes clearer as well as better to optimize by
the compiler.

[arnd@arndb.de: fix logic bug]
  Link: https://lkml.kernel.org/r/20230415081904.969049-1-arnd@kernel.org
Link: https://lkml.kernel.org/r/20230414080418.110236-1-arnd@kernel.org
Fixes: 9420f89d ("mm: move most of core MM initialization to mm/mm_init.c")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: SeongJae Park <sj@kernel.org>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/arc/mm/init.c

@@ -74,11 +74,6 @@ void __init early_init_dt_add_memory_arch(u64 base, u64 size)
 		base, TO_MB(size), !in_use ? "Not used":"");
 }
 
-bool arch_has_descending_max_zone_pfns(void)
-{
-	return !IS_ENABLED(CONFIG_ARC_HAS_PAE40);
-}
-
 /*
  * First memory setup routine called from setup_arch()
  * 1. setup swapper's mm @init_mm

include/linux/mm.h

@@ -3035,7 +3035,6 @@ extern void setup_per_cpu_pageset(void);
 extern int min_free_kbytes;
 extern int watermark_boost_factor;
 extern int watermark_scale_factor;
-extern bool arch_has_descending_max_zone_pfns(void);
 
 /* nommu.c */
 extern atomic_long_t mmap_pages_allocated;

mm/mm_init.c

@@ -1752,9 +1752,9 @@ static void __init free_area_init_memoryless_node(int nid)
  * Some architectures, e.g. ARC may have ZONE_HIGHMEM below ZONE_NORMAL. For
  * such cases we allow max_zone_pfn sorted in the descending order
  */
-bool __weak arch_has_descending_max_zone_pfns(void)
+static bool arch_has_descending_max_zone_pfns(void)
 {
-	return false;
+	return IS_ENABLED(CONFIG_ARC) && !IS_ENABLED(CONFIG_ARC_HAS_PAE40);
 }
 
 /**