Fix: StackAllocator Undefined Reference fix (#5650)

Co-authored-by: Kim Kulling <[email protected]>

code/Common/StackAllocator.h

@@ -88,6 +88,11 @@ private:
 
 } // namespace Assimp
 
+/// @brief Fixes an undefined reference error when linking in certain build environments.
+//         May throw warnings about needing stdc++17, but should compile without issues on modern compilers.
+inline const size_t Assimp::StackAllocator::g_maxBytesPerBlock;
+inline const size_t Assimp::StackAllocator::g_startBytesPerBlock;
+
 #include "StackAllocator.inl"
 
 #endif // include guard