build: add missing GCC condition for pragma

modules/features2d/src/sift.simd.hpp

@@ -829,14 +829,19 @@ else // CV_8U
         v_pack_store(dst + k, __pack01);
     }
 #endif
+
+#if defined(__GNUC__) && __GNUC__ >= 9
 // avoid warning "iteration 7 invokes undefined behavior" on Linux ARM64
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Waggressive-loop-optimizations"
+#endif
     for( ; k < len; k++ )
     {
         dst[k] = saturate_cast<uchar>(rawDst[k]*nrm2);
     }
+#if defined(__GNUC__) && __GNUC__ >= 9
 #pragma GCC diagnostic pop
+#endif
 }
 #else
     float* dst = dstMat.ptr<float>(row);