Code review feedback for DLL declimport/export (#214)

Author: walbourn

.azuredevops/policies/approvercountpolicy.yml

@@ -0,0 +1,20 @@
+name: approver_count
+description: Approver count policy for mscodehub/DirectXMesh/DirectXMesh repository
+resource: repository
+where: 
+configuration:
+  approverCountPolicySettings:
+    isBlocking: true
+    requireMinimumApproverCount: 1
+    creatorVoteCounts: false
+    allowDownvotes: false
+    sourcePushOptions:
+      resetOnSourcePush: false
+      requireVoteOnLastIteration: true
+      requireVoteOnEachIteration: false
+      resetRejectionsOnSourcePush: false
+    blockLastPusherVote: true
+    branchNames:
+    - refs/heads/release
+    - refs/heads/main
+    displayName: mscodehub/DirectXMesh/DirectXMesh Approver Count Policy

DirectXMesh/DirectXMesh.h

@@ -42,10 +42,18 @@
 
 #define DIRECTX_MESH_VERSION 168
 
-#ifdef DIRECTX_MESH_EXPORT
+#if defined(_WIN32) && defined(DIRECTX_MESH_EXPORT)
+#ifdef __GNUC__
+#define DIRECTX_MESH_API __attribute__ ((dllexport))
+#else
 #define DIRECTX_MESH_API __declspec(dllexport)
-#elif defined(DIRECTX_MESH_IMPORT)
+#endif
+#elif defined(_WIN32) && defined(DIRECTX_MESH_IMPORT)
+#ifdef __GNUC__
+#define DIRECTX_MESH_API __attribute__ ((dllimport))
+#else
 #define DIRECTX_MESH_API __declspec(dllimport)
+#endif
 #else
 #define DIRECTX_MESH_API
 #endif