crashdump: fix undefined reference to `elfcorehdr_addr'

fix build bug introduced by 95b68dec "calgary iommu: use the first
kernels TCE tables in kdump":

arch/x86/kernel/built-in.o: In function `calgary_iommu_init':
(.init.text+0x8399): undefined reference to `elfcorehdr_addr'
arch/x86/kernel/built-in.o: In function `calgary_iommu_init':
(.init.text+0x856c): undefined reference to `elfcorehdr_addr'
arch/x86/kernel/built-in.o: In function `detect_calgary':
(.init.text+0x8c68): undefined reference to `elfcorehdr_addr'
arch/x86/kernel/built-in.o: In function `detect_calgary':
(.init.text+0x8d0c): undefined reference to `elfcorehdr_addr'

make elfcorehdr_addr a generally available symbol.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/crash_dump.h

@@ -8,7 +8,13 @@
 #include <linux/proc_fs.h>
 
 #define ELFCORE_ADDR_MAX	(-1ULL)
+
+#ifdef CONFIG_PROC_VMCORE
 extern unsigned long long elfcorehdr_addr;
+#else
+static const unsigned long long elfcorehdr_addr = ELFCORE_ADDR_MAX;
+#endif
+
 extern ssize_t copy_oldmem_page(unsigned long, char *, size_t,
 						unsigned long, int);
 extern const struct file_operations proc_vmcore_operations;