[committed] libstdc++: Fix test failure with --disable-linux-futex

[Jonathan Wakely <jwakely@redhat.com>]

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As noted in PR 96817 this new test fails if the library is built without
futexes. That's expected of course, but we might as well fail more
obviously than a deadlock that eventually times out.

libstdc++-v3/ChangeLog:

	* testsuite/18_support/96817.cc: Fail fail if the library is
	configured to not use futexes.

Tested powerpc64le-linux. Committed to trunk.

I've just realised the changelog above should say "Fail fast", I'll
fix that in the ChangeLog tomorrow.



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commit 9c1125c121423a9948fa39e71ef89ba4059a2fad
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Nov 4 15:24:47 2020

    libstdc++: Fix test failure with --disable-linux-futex
    
    As noted in PR 96817 this new test fails if the library is built without
    futexes. That's expected of course, but we might as well fail more
    obviously than a deadlock that eventually times out.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/18_support/96817.cc: Fail fail if the library is
            configured to not use futexes.

diff --git a/libstdc++-v3/testsuite/18_support/96817.cc b/libstdc++-v3/testsuite/18_support/96817.cc
index f03329678313..4591a7288a57 100644
--- a/libstdc++-v3/testsuite/18_support/96817.cc
+++ b/libstdc++-v3/testsuite/18_support/96817.cc
@@ -24,6 +24,10 @@
 #include <exception>
 #include <stdlib.h>
 
+#ifndef _GLIBCXX_HAVE_LINUX_FUTEX
+# error "This test requries futex support in the library"
+#endif
+
 int init()
 {
 #if __has_include(<sys/single_threaded.h>)