Add a missing CERES_EXPORT to GradientChecker

Change-Id: Ib6b21354191b7ef5a0781cb3e53488144aa3f7b6

include/ceres/gradient_checker.h

diff --git a/include/ceres/gradient_checker.h b/include/ceres/gradient_checker.h
index 6d285da..c8ac729 100644
--- a/include/ceres/gradient_checker.h
+++ b/include/ceres/gradient_checker.h
@@ -64,7 +64,7 @@
 //
 // How to use: Fill in an array of pointers to parameter blocks for your
 // CostFunction, and then call Probe(). Check that the return value is 'true'.
-class GradientChecker {
+class CERES_EXPORT GradientChecker {
  public:
   // This will not take ownership of the cost function or local
   // parameterizations.
@@ -80,7 +80,7 @@
       const NumericDiffOptions& options);
 
   // Contains results from a call to Probe for later inspection.
-  struct ProbeResults {
+  struct CERES_EXPORT ProbeResults {
     // The return value of the cost function.
     bool return_value;