headers: properly decorate attributes

As pointed out here:
https://cygwin.com/ml/cygwin/2014-07/msg00371.html

any use of __attribute__ in a header that can be included by a user
should be namespace-safe, by decorating the attribute arguments with __
(while gcc does a lousy job at documenting it, ALL attributes have a __
counterpart, precisely so that public headers can use attributes without
risk of collision with macros belonging to user namespace).

* include/pthread.h: Decorate attribute names with __, for
namespace safety.
* include/cygwin/core_dump.h: Likewise.
* include/cygwin/cygwin_dll.h: Likewise.
* include/sys/cygwin.h: Likewise.
* include/sys/strace.h: Likewise.

winsup/cygwin/include/cygwin/core_dump.h

@@ -1,6 +1,6 @@
 /* core_dump.h
 
-   Copyright 1999, 2000, 2001 Red Hat, Inc.
+   Copyright 1999, 2000, 2001, 2014 Red Hat, Inc.
 
    Written by Egor Duda <deo@logos-m.ru>
 
@@ -27,7 +27,7 @@ struct win32_core_process_info
   char command_line[1];
 }
 #ifdef __GNUC__
-  __attribute__ ((packed))
+  __attribute__ ((__packed__))
 #endif
 ;
 
@@ -38,7 +38,7 @@ struct win32_core_thread_info
   CONTEXT thread_context;
 }
 #ifdef __GNUC__
-  __attribute__ ((packed))
+  __attribute__ ((__packed__))
 #endif
 ;
 
@@ -49,7 +49,7 @@ struct win32_core_module_info
   char module_name[1];
 }
 #ifdef __GNUC__
-  __attribute__ ((packed))
+  __attribute__ ((__packed__))
 #endif
 ;
 
@@ -64,7 +64,7 @@ struct win32_pstatus
     } data ;
 }
 #ifdef __GNUC__
-  __attribute__ ((packed))
+  __attribute__ ((__packed__))
 #endif
 ;
 

winsup/cygwin/include/cygwin/cygwin_dll.h

@@ -1,6 +1,6 @@
 /* cygwin_dll.h
 
-   Copyright 1998, 1999, 2000, 2001, 2009, 2011, 2012, 2013 Red Hat, Inc.
+   Copyright 1998, 1999, 2000, 2001, 2009, 2011, 2012, 2013, 2014 Red Hat, Inc.
 
 This file is part of Cygwin.
 
@@ -35,9 +35,9 @@ static DWORD storedReason;						      \
 static void* storedPtr;							      \
 int __dynamically_loaded;						      \
 									      \
-static int __dllMain (int a __attribute__ ((unused)),			      \
-		      char **b __attribute__ ((unused)),		      \
-		      char **c __attribute__ ((unused)))		      \
+static int __dllMain (int a __attribute__ ((__unused__)),		      \
+		      char **b __attribute__ ((__unused__)),		      \
+		      char **c __attribute__ ((__unused__)))		      \
 {									      \
   return Entry (storedHandle, storedReason, storedPtr);		              \
 }									      \