Fix issue2045 which get a error case _mm256_set_m128d op not supported by gcc 7.x

Eigen/src/Core/arch/AVX/PacketMath.h

diff --git a/Eigen/src/Core/arch/AVX/PacketMath.h b/Eigen/src/Core/arch/AVX/PacketMath.h
index ae4c4aa..ae111c6 100644
--- a/Eigen/src/Core/arch/AVX/PacketMath.h
+++ b/Eigen/src/Core/arch/AVX/PacketMath.h
@@ -707,7 +707,8 @@
 #endif
   Packet2d exponent_lo = _mm_cvtepi32_pd(vec4i_swizzle1(lo, 0, 2, 1, 3));
   Packet2d exponent_hi = _mm_cvtepi32_pd(vec4i_swizzle1(hi, 0, 2, 1, 3));
-  exponent = _mm256_set_m128d(exponent_hi, exponent_lo);
+  exponent = _mm256_insertf128_pd(exponent, exponent_lo, 0);
+  exponent = _mm256_insertf128_pd(exponent, exponent_hi, 1);
 #endif  // EIGEN_VECTORIZE_AVX512DQ
   exponent = psub(exponent, cst_1022d);
   const Packet4d cst_mant_mask  = pset1frombits<Packet4d>(static_cast<uint64_t>(~0x7ff0000000000000ull));