[gcc r13-4528] libstdc++: Fix test that fails due to name clash with old glibc [PR107979]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:2a23b93f944fa78d4284eb5687051c224e5ab08f

commit r13-4528-g2a23b93f944fa78d4284eb5687051c224e5ab08f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Dec 5 21:44:26 2022 +0000

    libstdc++: Fix test that fails due to name clash with old glibc [PR107979]
    
    This test was recently modified to check that the library doesn't use
    __unused anywhere, because that's a macro in newlib. But it's also a
    macro in old versions of glibc, so the test now fails for those targets.
    Disable that check for those targets as well as for newlib.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/107979
            * testsuite/17_intro/names.cc: Do not check __unused on old
            Glibc versions.

Diff:
---
 libstdc++-v3/testsuite/17_intro/names.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/libstdc++-v3/testsuite/17_intro/names.cc b/libstdc++-v3/testsuite/17_intro/names.cc
index ffbb199797b..963f74c11f3 100644
--- a/libstdc++-v3/testsuite/17_intro/names.cc
+++ b/libstdc++-v3/testsuite/17_intro/names.cc
@@ -241,6 +241,13 @@
 #undef y
 #endif
 
+#ifdef __GLIBC_PREREQ
+#if ! __GLIBC_PREREQ(2, 19)
+// Glibc defines this prior to 2.19
+#undef __unused
+#endif
+#endif
+
 #if __has_include(<newlib.h>)
 // newlib's <sys/cdefs.h> defines these as macros.
 #undef __lockable