[gcc r13-5461] libstdc++: Fix up FAIL in 17_intro/names.cc on glibc < 2.19 [PR108568]

[gcc r13-5461] libstdc++: Fix up FAIL in 17_intro/names.cc on glibc < 2.19 [PR108568]

[Jakub Jelinek]

https://gcc.gnu.org/g:815e5740162d2d0b7b54031f72c201065016d58c

commit r13-5461-g815e5740162d2d0b7b54031f72c201065016d58c
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Jan 27 20:11:20 2023 +0100

    libstdc++: Fix up FAIL in 17_intro/names.cc on glibc < 2.19 [PR108568]
    
    On gcc112 which has glibc 2.17 I've noticed
    FAIL: 17_intro/names.cc (test for excess errors)
    FAIL: experimental/names.cc (test for excess errors)
    These are because glibc < 2.19 used __unused as field member of various structs,
    including mcontext_t in sys/ucontext.h on ppc64le.
    This was changed in glibc with
    https://gcc.gnu.org/pipermail/libc-alpha/2013-November/045766.html
    names.cc even has
     #ifdef __GLIBC_PREREQ
     #if ! __GLIBC_PREREQ(2, 19)
     // Glibc defines this prior to 2.19
     #undef __unused
     #endif
     #endif
    for it, but it doesn't work.  The reason is that __GLIBC_PREREQ is defined in
    <features.h> but nothing included that header before this spot (it is included later
    from bits/stdc++.h).
    
    The following patch on Linux/Hurd conditionally includes features.h to get
    the needed macros before deciding if __unused should be undefined or not.
    If needed, I could use __GLIBC_PREREQ then but would need to check if it is
    defined and between 1996 and 1999 it wasn't.
    
    2023-01-27  Jakub Jelinek  <jakub@redhat.com>
    
            PR libstdc++/108568
            * testsuite/17_intro/names.cc (__unused): For linux or GNU hurd
            include features.h if present and then check __GLIBC__ and
            __GLIBC_MINOR__ macros for glibc prior to 2.19, instead of testing
            __GLIBC_PREREQ which isn't defined yet.

Diff:
---
 libstdc++-v3/testsuite/17_intro/names.cc | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/testsuite/17_intro/names.cc b/libstdc++-v3/testsuite/17_intro/names.cc
index 6fe9350aec6..d3e0db9bab6 100644
--- a/libstdc++-v3/testsuite/17_intro/names.cc
+++ b/libstdc++-v3/testsuite/17_intro/names.cc
@@ -252,12 +252,15 @@
 #undef y
 #endif
 
-#ifdef __GLIBC_PREREQ
-#if ! __GLIBC_PREREQ(2, 19)
+#if defined (__linux__) || defined (__gnu_hurd__)
+#if __has_include(<features.h>)
+#include <features.h>
+#if __GLIBC__ == 2 && __GLIBC_MINOR__ < 19
 // Glibc defines this prior to 2.19
 #undef __unused
 #endif
 #endif
+#endif
 
 #if __has_include(<newlib.h>)
 // newlib's <sys/cdefs.h> defines these as macros.