Add C++ guards around generated headers

Commit 0625a74d69 moved the C++ guards
after the inclusion of the generated headers, which was an unintended
behavioural change and now requires header guards around the inclusion
of Epoxy headers.

Fixes: #106

include/epoxy/egl.h

@@ -41,10 +41,10 @@
 #define __eglext_h_
 #endif
 
-#include "epoxy/egl_generated.h"
-
 EPOXY_BEGIN_DECLS
 
+#include "epoxy/egl_generated.h"
+
 EPOXY_PUBLIC bool epoxy_has_egl_extension(EGLDisplay dpy, const char *extension);
 EPOXY_PUBLIC int epoxy_egl_version(EGLDisplay dpy);
 EPOXY_PUBLIC bool epoxy_has_egl(void);

include/epoxy/gl.h

@@ -84,10 +84,10 @@
 #define GLAPIENTRYP GLAPIENTRY *
 #endif
 
-#include "epoxy/gl_generated.h"
-
 EPOXY_BEGIN_DECLS
 
+#include "epoxy/gl_generated.h"
+
 EPOXY_PUBLIC bool epoxy_has_gl_extension(const char *extension);
 EPOXY_PUBLIC bool epoxy_is_desktop_gl(void);
 EPOXY_PUBLIC int epoxy_gl_version(void);

include/epoxy/glx.h

@@ -44,10 +44,10 @@
 #define __glxext_h_
 #endif
 
-#include "epoxy/glx_generated.h"
-
 EPOXY_BEGIN_DECLS
 
+#include "epoxy/glx_generated.h"
+
 EPOXY_PUBLIC bool epoxy_has_glx_extension(Display *dpy, int screen, const char *extension);
 EPOXY_PUBLIC int epoxy_glx_version(Display *dpy, int screen);
 EPOXY_PUBLIC bool epoxy_has_glx(Display *dpy);

include/epoxy/wgl.h

@@ -49,10 +49,10 @@
 #define wglUseFontBitmaps wglUseFontBitmapsA
 #endif
 
-#include "epoxy/wgl_generated.h"
-
 EPOXY_BEGIN_DECLS
 
+#include "epoxy/wgl_generated.h"
+
 EPOXY_PUBLIC bool epoxy_has_wgl_extension(HDC hdc, const char *extension);
 EPOXY_PUBLIC void epoxy_handle_external_wglMakeCurrent(void);