[gcc r12-5013] libstdc++: only define _GLIBCXX_HAVE_TLS for VxWorks >= 6.6

[Rasmus Villemoes <villemoes@gcc.gnu.org>]

https://gcc.gnu.org/g:cc6b8cd9a21b363815998b11e5cc7529557a9ce5

commit r12-5013-gcc6b8cd9a21b363815998b11e5cc7529557a9ce5
Author: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Date:   Fri Nov 5 15:37:33 2021 +0100

    libstdc++: only define _GLIBCXX_HAVE_TLS for VxWorks >= 6.6
    
    According to
    https://gcc.gnu.org/legacy-ml/gcc-patches/2008-03/msg01698.html, the
    TLS support, including the __tls_lookup function, was added to VxWorks
    in 6.6.
    
    It certainly doesn't exist on our VxWorks 5 platform, but the fallback
    code in eh_globals.cc using __gthread_key_create() etc. used to work
    just fine.
    
    libstdc++-v3/ChangeLog:
    
            * config/os/vxworks/os_defines.h (_GLIBCXX_HAVE_TLS): Only
            define for VxWorks >= 6.6.

Diff:
---
 libstdc++-v3/config/os/vxworks/os_defines.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/config/os/vxworks/os_defines.h b/libstdc++-v3/config/os/vxworks/os_defines.h
index c881b2b4b9e..75a68bc605b 100644
--- a/libstdc++-v3/config/os/vxworks/os_defines.h
+++ b/libstdc++-v3/config/os/vxworks/os_defines.h
@@ -45,8 +45,10 @@
 #define _GLIBCXX_USE_WEAK_REF 0
 #endif
 
-// We support TLS on VxWorks (either directly or with emutls)
+// We support TLS on VxWorks >= 6.6 (either directly or with emutls)
+#if !_VXWORKS_PRE(6, 6)
 #define _GLIBCXX_HAVE_TLS 1
+#endif
 
 // VxWorks7 comes with a DinkumWare library and the system headers which we
 // are going to include for libstdc++ have a few related intrinsic