Unify symbol visibility configuration for all compilers

This makes it possible to build unit tests with shared libraries on MSVC.

Change-Id: I1db66a80b2c78c4f3d354e35235244d17bac9809

internal/ceres/block_random_access_matrix.h

@@ -35,6 +35,8 @@
 
 #include <mutex>
 
+#include "ceres/internal/port.h"
+
 namespace ceres {
 namespace internal {
 
@@ -91,7 +93,7 @@ struct CellInfo {
   std::mutex m;
 };
 
-class BlockRandomAccessMatrix {
+class CERES_EXPORT_INTERNAL BlockRandomAccessMatrix {
  public:
   virtual ~BlockRandomAccessMatrix();