Imported from dev-cpp/eigen to use with bundled's (ideally would
unbundle but rather not w/ Qt unless there is an upstream-supported
cmake switch, is likely broken w/ the upcoming eigen version too).

This is a backport from eigen upstream, so should no longer be needed
whenever there is a bump (not in a release as of the writing of this)
and it is updated here.

https://bugs.gentoo.org/943402
https://bugs.gentoo.org/936107
https://gitlab.com/libeigen/eigen/-/merge_requests/1028
--- a/src/3rdparty/eigen/Eigen/Core
+++ b/src/3rdparty/eigen/Eigen/Core
@@ -348,3 +348,3 @@
 
-#if defined(EIGEN_VECTORIZE_ALTIVEC) || defined(EIGEN_VECTORIZE_VSX)
+#if defined(EIGEN_VECTORIZE_VSX)
   #include "src/Core/arch/AltiVec/MatrixProduct.h"
--- a/src/3rdparty/eigen/Eigen/src/Core/arch/AltiVec/Complex.h
+++ b/src/3rdparty/eigen/Eigen/src/Core/arch/AltiVec/Complex.h
@@ -102,2 +102,3 @@
     HasMax    = 0,
+    HasSqrt   = 1,
 #ifdef __VSX__
@@ -322,2 +323,3 @@
     HasMax    = 0,
+    HasSqrt   = 1,
     HasSetLinear = 0
--- a/src/3rdparty/eigen/Eigen/src/Core/arch/AltiVec/MathFunctions.h
+++ b/src/3rdparty/eigen/Eigen/src/Core/arch/AltiVec/MathFunctions.h
@@ -42,2 +42,3 @@
 
+#ifdef __VSX__
 #ifndef EIGEN_COMP_CLANG
@@ -48,6 +49,3 @@
 }
-#endif
 
-#ifdef __VSX__
-#ifndef EIGEN_COMP_CLANG
 template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS EIGEN_UNUSED
@@ -76,2 +74,22 @@
 }
+
+template<> EIGEN_STRONG_INLINE Packet8bf psqrt<Packet8bf> (const Packet8bf& a){
+  BF16_TO_F32_UNARY_OP_WRAPPER(psqrt<Packet4f>, a);
+}
+
+#ifndef EIGEN_COMP_CLANG
+template<> EIGEN_STRONG_INLINE Packet8bf prsqrt<Packet8bf> (const Packet8bf& a){
+  BF16_TO_F32_UNARY_OP_WRAPPER(prsqrt<Packet4f>, a);
+}
+#endif
+#else
+template<> EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
+Packet4f psqrt<Packet4f>(const Packet4f& x)
+{
+  Packet4f a;
+  for (Index i = 0; i < packet_traits<float>::size; i++) {
+    a[i] = numext::sqrt(x[i]);
+  }
+  return a;
+}
 #endif
--- a/src/3rdparty/eigen/Eigen/src/Core/arch/AltiVec/PacketMath.h
+++ b/src/3rdparty/eigen/Eigen/src/Core/arch/AltiVec/PacketMath.h
@@ -177,2 +177,5 @@
 #endif
+    HasTanh = EIGEN_FAST_MATH,
+    HasErf = EIGEN_FAST_MATH,
+    HasRint = 1,
 #else
@@ -180,4 +183,5 @@
     HasRsqrt = 0,
-    HasTanh = EIGEN_FAST_MATH,
-    HasErf = EIGEN_FAST_MATH,
+    HasTanh = 0,
+    HasErf = 0,
+    HasRint = 0,
 #endif
@@ -186,3 +190,2 @@
     HasCeil = 1,
-    HasRint = 1,
     HasNegate = 1,
@@ -219,2 +222,3 @@
 #endif
+    HasRint = 1,
 #else
@@ -222,5 +226,6 @@
     HasRsqrt = 0,
-    HasTanh = EIGEN_FAST_MATH,
-    HasErf = EIGEN_FAST_MATH,
+    HasRint = 0,
 #endif
+    HasTanh = 0,
+    HasErf = 0,
     HasRound = 1,
@@ -228,3 +233,2 @@
     HasCeil = 1,
-    HasRint = 1,
     HasNegate = 1,
@@ -874,15 +878,25 @@
 
+#ifdef __VSX__
 template<> EIGEN_STRONG_INLINE Packet4i pcmp_le(const Packet4i& a, const Packet4i& b) { return reinterpret_cast<Packet4i>(vec_cmple(a,b)); }
+#endif
 template<> EIGEN_STRONG_INLINE Packet4i pcmp_lt(const Packet4i& a, const Packet4i& b) { return reinterpret_cast<Packet4i>(vec_cmplt(a,b)); }
 template<> EIGEN_STRONG_INLINE Packet4i pcmp_eq(const Packet4i& a, const Packet4i& b) { return reinterpret_cast<Packet4i>(vec_cmpeq(a,b)); }
+#ifdef __VSX__
 template<> EIGEN_STRONG_INLINE Packet8s pcmp_le(const Packet8s& a, const Packet8s& b) { return reinterpret_cast<Packet8s>(vec_cmple(a,b)); }
+#endif
 template<> EIGEN_STRONG_INLINE Packet8s pcmp_lt(const Packet8s& a, const Packet8s& b) { return reinterpret_cast<Packet8s>(vec_cmplt(a,b)); }
 template<> EIGEN_STRONG_INLINE Packet8s pcmp_eq(const Packet8s& a, const Packet8s& b) { return reinterpret_cast<Packet8s>(vec_cmpeq(a,b)); }
+#ifdef __VSX__
 template<> EIGEN_STRONG_INLINE Packet8us pcmp_le(const Packet8us& a, const Packet8us& b) { return reinterpret_cast<Packet8us>(vec_cmple(a,b)); }
+#endif
 template<> EIGEN_STRONG_INLINE Packet8us pcmp_lt(const Packet8us& a, const Packet8us& b) { return reinterpret_cast<Packet8us>(vec_cmplt(a,b)); }
 template<> EIGEN_STRONG_INLINE Packet8us pcmp_eq(const Packet8us& a, const Packet8us& b) { return reinterpret_cast<Packet8us>(vec_cmpeq(a,b)); }
+#ifdef __VSX__
 template<> EIGEN_STRONG_INLINE Packet16c pcmp_le(const Packet16c& a, const Packet16c& b) { return reinterpret_cast<Packet16c>(vec_cmple(a,b)); }
+#endif
 template<> EIGEN_STRONG_INLINE Packet16c pcmp_lt(const Packet16c& a, const Packet16c& b) { return reinterpret_cast<Packet16c>(vec_cmplt(a,b)); }
 template<> EIGEN_STRONG_INLINE Packet16c pcmp_eq(const Packet16c& a, const Packet16c& b) { return reinterpret_cast<Packet16c>(vec_cmpeq(a,b)); }
+#ifdef __VSX__
 template<> EIGEN_STRONG_INLINE Packet16uc pcmp_le(const Packet16uc& a, const Packet16uc& b) { return reinterpret_cast<Packet16uc>(vec_cmple(a,b)); }
+#endif
 template<> EIGEN_STRONG_INLINE Packet16uc pcmp_lt(const Packet16uc& a, const Packet16uc& b) { return reinterpret_cast<Packet16uc>(vec_cmplt(a,b)); }
@@ -939,2 +953,3 @@
 template<> EIGEN_STRONG_INLINE Packet4f pfloor<Packet4f>(const Packet4f& a) { return vec_floor(a); }
+#ifdef __VSX__
 template<> EIGEN_STRONG_INLINE Packet4f print<Packet4f>(const Packet4f& a)
@@ -949,2 +964,3 @@
 }
+#endif
 
@@ -1343,8 +1359,2 @@
 
-template<> EIGEN_STRONG_INLINE Packet8bf psqrt<Packet8bf> (const Packet8bf& a){
-  BF16_TO_F32_UNARY_OP_WRAPPER(vec_sqrt, a);
-}
-template<> EIGEN_STRONG_INLINE Packet8bf prsqrt<Packet8bf> (const Packet8bf& a){
-  BF16_TO_F32_UNARY_OP_WRAPPER(prsqrt<Packet4f>, a);
-}
 template<> EIGEN_STRONG_INLINE Packet8bf pexp<Packet8bf> (const Packet8bf& a){
@@ -1392,2 +1402,3 @@
 }
+#ifdef __VSX__
 template<> EIGEN_STRONG_INLINE Packet8bf print<Packet8bf> (const Packet8bf& a){
@@ -1395,2 +1406,3 @@
 }
+#endif
 template<> EIGEN_STRONG_INLINE Packet8bf pmadd(const Packet8bf& a, const Packet8bf& b, const Packet8bf& c) {