[core] mark log_error_write*() funcs cold

src/log.h

@@ -10,7 +10,10 @@ int log_clock_gettime_realtime (struct timespec *ts);
 
 ssize_t write_all(int fd, const void* buf, size_t count);
 
+__attribute_cold__
 int log_error_write(server *srv, const char *filename, unsigned int line, const char *fmt, ...);
+
+__attribute_cold__
 int log_error_write_multiline_buffer(server *srv, const char *filename, unsigned int line, buffer *multiline, const char *fmt, ...);
 
 #endif