[PATCH v2] wchar: Define va_list for POSIX (BZ #30035)

[Adhemerval Zanella]

This was uncovered by a recent clang change [1].  Different than ISO C,
POSIX states that va_list should be exported by wchar.h [2].

Checked on x86_64-linux-gnu and aarch64-linux-gnu.

[1] https://reviews.llvm.org/D137268
[2] https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/basedefs/wchar.h.html
---
 conform/data/wchar.h-data |  3 +++
 wcsmbs/wchar.h            | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/conform/data/wchar.h-data b/conform/data/wchar.h-data
index e414651a33..0af74e14bc 100644
--- a/conform/data/wchar.h-data
+++ b/conform/data/wchar.h-data
@@ -15,6 +15,9 @@ type size_t
 type locale_t
 # endif
 tag {struct tm}
+# if !defined ISO99 && !defined ISO11 && !defined UNIX98
+type va_list
+# endif
 
 function wint_t btowc (int)
 function int fwprintf (FILE*, const wchar_t*, ...)
diff --git a/wcsmbs/wchar.h b/wcsmbs/wchar.h
index 69e920b8c2..ca145bb8d2 100644
--- a/wcsmbs/wchar.h
+++ b/wcsmbs/wchar.h
@@ -37,6 +37,17 @@
 #define __need___va_list
 #include <stdarg.h>
 
+#if defined __USE_XOPEN2K || defined __USE_XOPEN2K8
+# ifdef __GNUC__
+#  ifndef _VA_LIST_DEFINED
+typedef __gnuc_va_list va_list;
+#   define _VA_LIST_DEFINED
+#  endif
+# else
+#  include <stdarg.h>
+# endif
+#endif
+
 #include <bits/wchar.h>
 #include <bits/types/wint_t.h>
 #include <bits/types/mbstate_t.h>
-- 
2.34.1