Fix XPG4 bsd_signal namespace (bug 21552).

bsd_signal was added in XPG4.2, so should be declared for
__USE_XOPEN_EXTENDED, instead of the present __USE_XOPEN condition.
This patch fixes the condition accordingly.

Tested for x86_64.

	[BZ #21552]
	* signal/signal.h (bsd_signal): Declare if [__USE_XOPEN_EXTENDED],
	not [__USE_XOPEN].
	* conform/Makefile (test-xfail-XPG4/signal.h/conform): Remove.

ChangeLog

@@ -1,5 +1,10 @@
 2017-06-12  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #21552]
+	* signal/signal.h (bsd_signal): Declare if [__USE_XOPEN_EXTENDED],
+	not [__USE_XOPEN].
+	* conform/Makefile (test-xfail-XPG4/signal.h/conform): Remove.
+
 	[BZ #21550]
 	* signal/signal.h (sigwait): Only declare if [__USE_POSIX199506].
 

conform/Makefile

@@ -161,7 +161,6 @@ test-xfail-XOPEN2K/ndbm.h/conform = yes
 test-xfail-XOPEN2K8/ndbm.h/conform = yes
 
 # Unsorted expected failures.
-test-xfail-XPG4/signal.h/conform = yes
 test-xfail-XPG42/signal.h/conform = yes
 test-xfail-XPG42/sys/wait.h/conform = yes
 test-xfail-XPG42/ucontext.h/conform = yes

signal/signal.h

@@ -94,7 +94,7 @@ extern __sighandler_t __REDIRECT_NTH (signal,
 # endif
 #endif
 
-#if defined __USE_XOPEN && !defined __USE_XOPEN2K8
+#if defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8
 /* The X/Open definition of `signal' conflicts with the BSD version.
    So they defined another function `bsd_signal'.  */
 extern __sighandler_t bsd_signal (int __sig, __sighandler_t __handler)