reftests: Fix building on Visual Studio

We need to mark the prototypes in the headers so that they get exported
properly from the reftest DLLs that we build, so that the reftest DLLs
and program will link properly.  Include gtk-reftest.h in
reftest-snapshot.c so that the compiler picks up the export directives
as needed.

testsuite/reftests/gtk-reftest.h

@@ -21,7 +21,10 @@
 G_BEGIN_DECLS
 
 /* reftest-snapshot.c */
+G_MODULE_EXPORT
 void reftest_inhibit_snapshot   (void);
+
+G_MODULE_EXPORT
 void reftest_uninhibit_snapshot (void);
 
 G_END_DECLS

testsuite/reftests/reftest-compare.h

@@ -22,6 +22,7 @@
 
 G_BEGIN_DECLS
 
+G_MODULE_EXPORT
 cairo_surface_t *       reftest_compare_surfaces        (cairo_surface_t        *surface1,
                                                          cairo_surface_t        *surface2);
 

testsuite/reftests/reftest-module.h

@@ -24,13 +24,19 @@ G_BEGIN_DECLS
 
 typedef struct _ReftestModule ReftestModule;
 
+G_MODULE_EXPORT
 ReftestModule * reftest_module_new              (const char     *directory,
                                                  const char     *module_name);
+G_MODULE_EXPORT
 ReftestModule * reftest_module_new_self         (void);
 
+G_MODULE_EXPORT
 ReftestModule * reftest_module_ref              (ReftestModule  *module);
+
+G_MODULE_EXPORT
 void            reftest_module_unref            (ReftestModule  *module);
 
+G_MODULE_EXPORT
 GCallback       reftest_module_lookup           (ReftestModule  *module,
                                                  const char     *function_name);
 

testsuite/reftests/reftest-snapshot.c

@@ -23,6 +23,7 @@
 #include "reftest-snapshot.h"
 
 #include "reftest-module.h"
+#include "gtk-reftest.h"
 
 #include <string.h>
 

testsuite/reftests/reftest-snapshot.h

@@ -22,6 +22,7 @@
 
 G_BEGIN_DECLS
 
+G_MODULE_EXPORT
 cairo_surface_t *       reftest_snapshot_ui_file                (const char     *ui_file);
 
 G_END_DECLS