bug #1744: fix compilation with MSVC 2017 and AVX512, plog1p/pexpm1 require plog/pexp, but the later was disabled on some compilers

Eigen/src/Core/arch/AVX512/MathFunctions.h

diff --git a/Eigen/src/Core/arch/AVX512/MathFunctions.h b/Eigen/src/Core/arch/AVX512/MathFunctions.h
index 99946cd..273c22c 100644
--- a/Eigen/src/Core/arch/AVX512/MathFunctions.h
+++ b/Eigen/src/Core/arch/AVX512/MathFunctions.h
@@ -378,6 +378,19 @@
   return _mm512_rsqrt28_ps(x);
 }
 #endif
+
+#if defined(EIGEN_VECTORIZE_AVX512DQ)
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
+Packet16f plog1p<Packet16f>(const Packet16f& _x) {
+  return generic_plog1p(_x);
+}
+
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
+Packet16f pexpm1<Packet16f>(const Packet16f& _x) {
+  return generic_expm1(_x);
+}
+#endif
+
 #endif
 
 
@@ -393,18 +406,6 @@
   return pcos_float(_x);
 }
 
-#if defined(EIGEN_VECTORIZE_AVX512DQ)
-template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
-Packet16f plog1p<Packet16f>(const Packet16f& _x) {
-  return generic_plog1p(_x);
-}
-
-template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
-Packet16f pexpm1<Packet16f>(const Packet16f& _x) {
-  return generic_expm1(_x);
-}
-#endif
-
 template <>
 EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED Packet16f
 ptanh<Packet16f>(const Packet16f& _x) {