A few visibility changes needed for linking to libpbd (when building with MSVC)

libs/pbd/pbd/glib_event_source.h

@@ -5,7 +5,7 @@
 
 #include <glibmm/main.h>
 
-class GlibEventLoopSource : public Glib::Source
+class LIBPBD_API GlibEventLoopSource : public Glib::Source
 {
   public:
 	GlibEventLoopSource () {};
@@ -16,7 +16,7 @@ class GlibEventLoopSource : public Glib::Source
 };
 
 
-class GlibEventLoopCallback : public GlibEventLoopSource
+class LIBPBD_API GlibEventLoopCallback : public GlibEventLoopSource
 {
   public:
 	GlibEventLoopCallback (boost::function<void()> callback) : _callback (callback) {}

libs/pbd/pbd/pcg_rand.h

@@ -20,6 +20,7 @@
 #define _pbd_pcg_rand_
 
 #include <stdint.h>
+#include "pbd/libpbd_visibility.h"
 
 namespace PBD
 {
@@ -29,7 +30,7 @@ namespace PBD
  * To be used in cases where an efficient and realtime-safe random
  * generator is needed.
  */
-class PCGRand
+class LIBPBD_API PCGRand
 {
 public:
 	PCGRand ();