fix linking errors with multiply defined functions

Eigen/src/Core/GenericPacketMath.h

diff --git a/Eigen/src/Core/GenericPacketMath.h b/Eigen/src/Core/GenericPacketMath.h
index c655511..77cd484 100644
--- a/Eigen/src/Core/GenericPacketMath.h
+++ b/Eigen/src/Core/GenericPacketMath.h
@@ -210,19 +210,24 @@
 ***************************/
 
 /** \internal \returns the sin of \a a (coeff-wise) */
-template<typename Packet> inline static Packet ei_psin(const Packet& a) { return ei_sin(a); }
+template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
+Packet ei_psin(const Packet& a) { return ei_sin(a); }
 
 /** \internal \returns the cos of \a a (coeff-wise) */
-template<typename Packet> inline static Packet ei_pcos(const Packet& a) { return ei_cos(a); }
+template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
+Packet ei_pcos(const Packet& a) { return ei_cos(a); }
 
 /** \internal \returns the exp of \a a (coeff-wise) */
-template<typename Packet> inline static Packet ei_pexp(const Packet& a) { return ei_exp(a); }
+template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
+Packet ei_pexp(const Packet& a) { return ei_exp(a); }
 
 /** \internal \returns the log of \a a (coeff-wise) */
-template<typename Packet> inline static Packet ei_plog(const Packet& a) { return ei_log(a); }
+template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
+Packet ei_plog(const Packet& a) { return ei_log(a); }
 
 /** \internal \returns the square-root of \a a (coeff-wise) */
-template<typename Packet> inline static Packet ei_psqrt(const Packet& a) { return ei_sqrt(a); }
+template<typename Packet> EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
+Packet ei_psqrt(const Packet& a) { return ei_sqrt(a); }
 
 /***************************************************************************
 * The following functions might not have to be overwritten for vectorized types

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

diff --git a/Eigen/src/Core/arch/SSE/MathFunctions.h b/Eigen/src/Core/arch/SSE/MathFunctions.h
index 79f9e39..3d75a4e 100644
--- a/Eigen/src/Core/arch/SSE/MathFunctions.h
+++ b/Eigen/src/Core/arch/SSE/MathFunctions.h
@@ -30,7 +30,7 @@
 #ifndef EIGEN_MATH_FUNCTIONS_SSE_H
 #define EIGEN_MATH_FUNCTIONS_SSE_H
 
-template<> EIGEN_DONT_INLINE EIGEN_UNUSED
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
 Packet4f ei_plog<Packet4f>(const Packet4f& _x)
 {
   Packet4f x = _x;
@@ -110,7 +110,7 @@
   return _mm_or_ps(x, invalid_mask); // negative arg will be NAN
 }
 
-template<> EIGEN_DONT_INLINE EIGEN_UNUSED
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
 Packet4f ei_pexp<Packet4f>(const Packet4f& _x)
 {
   Packet4f x = _x;
@@ -185,7 +185,7 @@
    surprising but correct result.
 */
 
-template<> EIGEN_DONT_INLINE EIGEN_UNUSED
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
 Packet4f ei_psin<Packet4f>(const Packet4f& _x)
 {
   Packet4f x = _x;
@@ -286,7 +286,7 @@
 }
 
 /* almost the same as ei_psin */
-template<> EIGEN_DONT_INLINE EIGEN_UNUSED
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
 Packet4f ei_pcos<Packet4f>(const Packet4f& _x)
 {
   Packet4f x = _x;
@@ -375,7 +375,7 @@
 
 // This is Quake3's fast inverse square root.
 // For detail see here: http://www.beyond3d.com/content/articles/8/
-template<> EIGEN_UNUSED
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
 Packet4f ei_psqrt<Packet4f>(const Packet4f& _x)
 {
 	Packet4f half = ei_pmul(_x, ei_pset1(.5f));

Eigen/src/Core/util/Macros.h

diff --git a/Eigen/src/Core/util/Macros.h b/Eigen/src/Core/util/Macros.h
index 3c033d1..875452e 100644
--- a/Eigen/src/Core/util/Macros.h
+++ b/Eigen/src/Core/util/Macros.h
@@ -162,6 +162,13 @@
 #define EIGEN_DONT_INLINE
 #endif
 
+// this macro allows to get rid of linking errors about multiply defined functions.
+//  - static is not very good because it prevents definitions from different object files to be merged.
+//           So static causes the resulting linked executable to be bloated with multiple copies of the same function.
+//  - inline is not perfect either as it unwantedly hints the compiler toward inlining the function.
+#define EIGEN_DECLARE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
+#define EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS inline
+
 #if (defined __GNUC__)
 #define EIGEN_DEPRECATED __attribute__((deprecated))
 #elif (defined _MSC_VER)