Fix compilation and warnings in shared libraries.

Include/RmlUi/Core/Transform.h

@@ -31,11 +31,11 @@
 
 #include "Header.h"
 #include "Types.h"
+#include "TransformPrimitive.h"
 
 namespace Rml {
 
 class Property;
-struct TransformPrimitive;
 
 /**
 	The Transform class holds the information parsed from an element's `transform' property.

Include/RmlUi/Core/TransformPrimitive.h

@@ -47,7 +47,7 @@ struct RMLUICORE_API NumericValue {
 
 // A resolved primitive has values that are always independent of an element's properties or layout.
 template< size_t N >
-struct ResolvedPrimitive
+struct RMLUICORE_API ResolvedPrimitive
 {
 	std::array<float, N> values;
 
@@ -61,7 +61,7 @@ protected:
 
 // An unresolved primitive may have values that depend on the final layout of a given element, such as its width.
 template< size_t N >
-struct UnresolvedPrimitive
+struct RMLUICORE_API UnresolvedPrimitive
 {
 	std::array<NumericValue, N> values;