Fix `#ifdef __cplusplus` for blocks `extern "C"` in config.h.cmake.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit e9571392f6)

config.h.cmake

@@ -1144,6 +1144,7 @@ __END_DECLS
 #endif
 #ifdef __cplusplus
 extern "C"
+{
 #endif
 #if !defined(HAVE_VSNPRINTF_PROTO)
 int vsnprintf(char *str, size_t n, char const *fmt, va_list ap);
@@ -1152,7 +1153,7 @@ int vsnprintf(char *str, size_t n, char const *fmt, va_list ap);
 int snprintf(char *str, size_t n, char const *fmt, ...);
 #endif
 #ifdef __cplusplus
-extern "C"
+}
 #endif
 #endif
 
@@ -1213,7 +1214,10 @@ extern "C"
 #define HAVE_SETEUID_FAKE
 #ifdef __cplusplus
 extern "C"
+{
 #endif
 int seteuid(INT32_BASETYPE euid); /* defined in fakes.c */
+#ifdef __cplusplus
+}
+#endif
 #endif
-