stepcompress: Modify check_expand() into check_push()

Add the new item at the same time as checking if there is space in the
queue.

Also, update the default optimization level of c_helper.so to O2 to
improve the compiled code layout.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/pyhelper.h

@@ -1,6 +1,9 @@
 #ifndef PYHELPER_H
 #define PYHELPER_H
 
+#define likely(x)       __builtin_expect(!!(x), 1)
+#define unlikely(x)     __builtin_expect(!!(x), 0)
+
 double get_monotonic(void);
 struct timespec fill_time(double time);
 void set_python_logging_callback(void (*func)(const char *));