RFA: Fix plugins/44459 1/2

[Joern Rennecke]

I have divided the patch set for this PR into two parts to allow separate
review:
This one, the first part, changes only gcc-plugin.h ; the purpose of this
file is quite obviously to provide a part of the plugin interface.

Bootstrapped and regression tested in 160389 with --enable-build-with-cxx

This patch by itself allows testsuite/gcc.dg/plugin/one_time_plugin.c to
be compiled with gcc into a functioning gcc plugin.

I would consider this patch alone a possible fix for PR 44459, although I'd
prefer to have more functionality supported, as would be available by  
combining
both parts of this patch set, or this part with a modified second part.

-------------- next part --------------
2010-06-08  Joern Rennecke  <joern.rennecke@embecosm.com>

	PR plugins/44459:
	* gcc-plugin.h: Encapsulate all declarations in extern "C".

Index: gcc-plugin.h
===================================================================
--- gcc-plugin.h	(revision 160389)
+++ gcc-plugin.h	(working copy)
@@ -38,6 +38,12 @@ enum plugin_event
   PLUGIN_EVENT_FIRST_DYNAMIC
 };
 
+/* All globals declared here have C linkage to reduce link compatibility
+   issues with implementation language choice and mangling.  */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 extern const char **plugin_event_name;
 
 struct plugin_argument
@@ -96,16 +102,10 @@ extern bool plugin_default_version_check
 typedef int (*plugin_init_func) (struct plugin_name_args *plugin_info,
                                  struct plugin_gcc_version *version);
 
-#ifdef __cplusplus
-extern "C" {
-#endif
 /* Declaration for "plugin_init" function so that it doesn't need to be
    duplicated in every plugin.  */
 extern int plugin_init (struct plugin_name_args *plugin_info,
                         struct plugin_gcc_version *version);
-#ifdef __cplusplus
-}
-#endif
 
 /* Function type for a plugin callback routine.
 
@@ -147,4 +147,8 @@ extern int unregister_callback (const ch
    -iplugindir program argument to cc1.  */
 extern const char* default_plugin_dir_name (void);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* GCC_PLUGIN_H */