[gobject-introspection] Update config.h.win32.in For Symbol Exporting

[Chun-wei Fan <fanchunwei src gnome org>]

commit d2ff2e13accf248b6d38aba0b0e310b31bf7cd3d
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Mon Jul 7 18:11:35 2014 +0800

    Update config.h.win32.in For Symbol Exporting
    
    This updates the pre-defined config.h.win32(.in) so that the Visual Studio
    builds can use so that symbols for libgirepository and the test libraries
    can be exported using the compiler directive __declspec(dllexport), without
    the use of .def files.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=732669

 config.h.win32.in |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)
---
diff --git a/config.h.win32.in b/config.h.win32.in
index 3bc66f2..f6e12cc 100644
--- a/config.h.win32.in
+++ b/config.h.win32.in
@@ -132,5 +132,12 @@
    `char[]'. */
 #define YYTEXT_POINTER 1
 
+/* defines how to decorate public symbols while building */
+#ifdef _MSC_VER
+#define _GI_EXTERN __declspec (dllexport) extern
+#else
+#define _GI_EXTERN __attribute__((visibility("default"))) __declspec (dllexport) extern
+#endif
+
 /* Define to empty if `const' does not conform to ANSI C. */
 /* #undef const */