[PATCH v2] libstdc++: Workaround glibc headers on ia64-linux

[Frank Scheiner]

We see:

```
FAIL: 17_intro/names.cc  -std=gnu++17 (test for excess errors)
FAIL: 17_intro/names_pstl.cc  -std=gnu++17 (test for excess errors)
FAIL: experimental/names.cc  -std=gnu++17 (test for excess errors)
```

...on ia64-linux.

This is due to:

* /usr/include/bits/sigcontext.h:32-38:
```
32 struct __ia64_fpreg
33   {
34     union
35       {
36         unsigned long bits[2];
37       } u;
38   } __attribute__ ((__aligned__ (16)));
```

* /usr/include/sys/ucontext.h:39-45:
```
  39 struct __ia64_fpreg_mcontext
  40   {
  41     union
  42       {
  43         unsigned long __ctx(bits)[2];
  44       } __ctx(u);
  45   } __attribute__ ((__aligned__ (16)));
```

...from glibc 2.39 (w/ia64 support re-added). See the discussion
starting on [1].

[1]: https://gcc.gnu.org/pipermail/gcc-patches/2024-June/654487.html

The following patch adds a workaround for this on the libstdc++
testsuite side.

Signed-off-by: Frank Scheiner <frank.scheiner@web.de>

---
v2: Fix typo in title.
  libstdc++-v3/testsuite/17_intro/names.cc | 6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/libstdc++-v3/testsuite/17_intro/names.cc
b/libstdc++-v3/testsuite/17_intro/names.cc
index 9b0ffcb50b2..b45aefe1ccf 100644
--- a/libstdc++-v3/testsuite/17_intro/names.cc
+++ b/libstdc++-v3/testsuite/17_intro/names.cc
@@ -265,6 +265,12 @@
  #undef j
  #endif

+#if defined (__linux__) && defined (__ia64__)
+// <bits/sigcontext.h> defines __ia64_fpreg::u
+// <sys/ucontext.h> defines __ia64_fpreg_mcontext::u
+#undef u
+#endif
+
  #if defined (__linux__) && defined (__powerpc__)
  // <asm/types.h> defines __vector128::u
  #undef u
--
2.45.2