Moved #include <complex.h> to after gtest.h

To avoid a #define conflict between <complex.h> and gtest.h when using
HIPcc compiler

Author: Balint Joo

tests/gauge_path_test.cpp

@@ -1,7 +1,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <complex.h>
 
 #include <quda.h>
 #include <host_utils.h>
@@ -12,6 +11,7 @@
 #include <gauge_path_quda.h>
 #include <timer.h>
 #include <gtest/gtest.h>
+#include <complex>
 
 static QudaGaugeFieldOrder gauge_order = QUDA_QDP_GAUGE_ORDER;