gstconfig.h: add GST_API_IMPORT define

This is for use by the various GST_*_API decorators and
will be what they get defined to when a library API is being
used by external users of that library (not the library itself
whilst it's being compiled).

In most cases it will simply map to a plain 'extern' but on
Windows with MSVC it will need to map to __declspec(dllimport).
For functions this is not strictly needed, but for exported
variables it is.

https://bugzilla.gnome.org/show_bug.cgi?id=797185

diff --git a/gst/gstconfig.h.in b/gst/gstconfig.h.in
index 33dfed1..cb92a2c 100644 (file)
--- a/gst/gstconfig.h.in
+++ b/gst/gstconfig.h.in
@@ -155,6 +155,12 @@
 # endif
 #endif
 
+#if defined(_MSC_VER) && !defined(GST_STATIC_COMPILATION)
+# define GST_API_IMPORT __declspec(dllimport) extern
+#else
+# define GST_API_IMPORT extern
+#endif
+
 #ifndef GST_API
 #define GST_API GST_EXPORT
 #endif