/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: 516fb7f2e73d ("/proc/module: use the same logic as /proc/kallsyms for address exposure")
Signed-off-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/kallsyms.h

···
 #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
···
 
 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 int lookup_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name)
 {
 	return -ERANGE;
+}
+
+static inline int kallsyms_show_value(void)
+{
+	return false;
 }
 
 /* Stupid that this does nothing, but I didn't create this mess. */