memblock tests: fix compilation errors

Do 'make -C tools/testing/memblock', get the following errors:

memblock.o: In function `memblock_find_in_range.constprop.9':
memblock.c:(.text+0x4651): undefined reference to `pr_warn_ratelimited'
memblock.o: In function `memblock_mark_mirror':
memblock.c:(.text+0x7171): undefined reference to `mirrored_kernelcore'

Fixes: 902c2d9 ("memblock: Disable mirror feature if kernelcore is not specified")
Fixes: 14d9a67 ("mm: Ratelimited mirrored memory related warning messages")

Signed-off-by: Liu Xinpeng <liuxp11@chinatelecom.cn>
Tested-by: Ma Wupeng <mawupeng1@huawei.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Link: https://lore.kernel.org/r/1658916453-26312-1-git-send-email-liuxp11@chinatelecom.cn

tools/testing/memblock/internal.h

@@ -9,6 +9,10 @@
 static int memblock_debug = 1;
 #endif
 
+#define pr_warn_ratelimited(fmt, ...)    printf(fmt, ##__VA_ARGS__)
+
+bool mirrored_kernelcore = false;
+
 struct page {};
 
 void memblock_free_pages(struct page *page, unsigned long pfn,