ancient GCC compatibility

Author: sunqm

pyscf/lib/dft/utils.c

@@ -52,11 +52,20 @@ void get_gga_vrho_gs(double complex *out, double complex *vrho_gs, double comple
     int i;
     int ngrid2 = 2 * ngrid;
     double complex fac = -2. * _Complex_I;
-    #pragma omp parallel for simd schedule(static)
+#pragma omp parallel
+{
+    double complex v;
+// ensure OpenMP 4.0
+#if defined _OPENMP && _OPENMP >= 201307
+    #pragma omp for simd schedule(static)
+#else
+    #pragma omp for schedule(static)
+#endif
     for (i = 0; i < ngrid; i++) {
-        out[i] = ( Gv[i*3]   * vsigma1_gs[i]
-                  +Gv[i*3+1] * vsigma1_gs[i+ngrid]
-                  +Gv[i*3+2] * vsigma1_gs[i+ngrid2]) * fac + vrho_gs[i];
-        out[i] *= weight;
+        v = ( Gv[i*3]   * vsigma1_gs[i]
+             +Gv[i*3+1] * vsigma1_gs[i+ngrid]
+             +Gv[i*3+2] * vsigma1_gs[i+ngrid2]) * fac + vrho_gs[i];
+        out[i] = v * weight;
     }
 }
+}