/proc/module: fix building without kallsyms

As reported by kernelci and other build bots, we now get a link
failure without CONFIG_KALLSYMS:

  module.c:(.text+0xf2c): undefined reference to `kallsyms_show_value'

This adds a dummy helper with the same name that can be used
for compilation. It's not entirely clear to me what this
should return for !CONFIG_KALLSYMS, I picked an unconditional
'false', which leads to the module address being unavailable
to user space.

Link: https://kernelci.org/build/mainline/branch/master/kernel/v4.14-5-g516fb7f2e73d/
Fixes: 516fb7f2 ("/proc/module: use the same logic as /proc/kallsyms for address exposure")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/kallsyms.h

@@ -14,8 +14,6 @@
 #define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s]") + (KSYM_NAME_LEN - 1) + \
 			 2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + 1)
 
-/* How and when do we show kallsyms values? */
-extern int kallsyms_show_value(void);
 #ifndef CONFIG_64BIT
 # define KALLSYM_FMT "%08lx"
 #else
@@ -54,6 +52,9 @@ extern void __print_symbol(const char *fmt, unsigned long address);
 int lookup_symbol_name(unsigned long addr, char *symname);
 int lookup_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
 
+/* How and when do we show kallsyms values? */
+extern int kallsyms_show_value(void);
+
 #else /* !CONFIG_KALLSYMS */
 
 static inline unsigned long kallsyms_lookup_name(const char *name)
@@ -112,6 +113,11 @@ static inline int lookup_symbol_attrs(unsigned long addr, unsigned long *size, u
 	return -ERANGE;
 }
 
+static inline int kallsyms_show_value(void)
+{
+	return false;
+}
+
 /* Stupid that this does nothing, but I didn't create this mess. */
 #define __print_symbol(fmt, addr)
 #endif /*CONFIG_KALLSYMS*/