xen/include: make a declaration of 'get_sec' visible where needed

A declaration for 'get_sec' is added in 'xen/include/xen/time.h' to
be available for every call site (in particular 'cper.h').
This also resolves a violation of MISRA C:2012 Rule 8.4.

Fixes: c8cb30cfc8 ("mce: Provide ERST interface")
Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/include/xen/cper.h

@@ -23,8 +23,7 @@
 
 #include <xen/types.h>
 #include <xen/string.h>
-
-extern unsigned long get_sec(void);
+#include <xen/time.h>
 
 typedef struct {
 	uint8_t b[16];

xen/include/xen/time.h

@@ -36,6 +36,7 @@ s_time_t get_s_time_fixed(u64 at_tick);
 s_time_t get_s_time(void);
 unsigned long get_localtime(struct domain *d);
 uint64_t get_localtime_us(struct domain *d);
+unsigned long get_sec(void);
 
 struct tm {
     int     tm_sec;         /* seconds */