[PATCH] Define _C99 in libstdc++ vxworks/os_defines.h

[Olivier Hainque <hainque@adacore.com>]

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Hello,

The attached patch for libstdc++ / VxWorks helps building
the library for old versions of the OS, as witnessed with
VxWorks 6.9 in particular.

It explicitly requests C99 features from old system headers,
on which libstc++ relies since at least c++98. The specific
issue that exposed this was a failure to compile

  libstdc++-v3/src/c++17/floating_to_chars.cc

for VxWorks 6.9 with a batch of errors such as:

  error: 'FP_NAN' was not declared in this scope

The missing definitions are provided by the
system headers with guards on _HAS_C9X, which gets
internally defined when _C99 is.

Ok to commit?

Thanks in advance!

2021-12-07  Olivier Hainque  <hainque@adacore.com>

libstdc++-v3/

	* config/os/vxworks/os_defines.h: #define _C99.

Olivier


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From f1051d0a9f2687fdf313b916d73b9b2d50e13ac2 Mon Sep 17 00:00:00 2001
From: Olivier Hainque <hainque@adacore.com>
Date: Fri, 19 Nov 2021 14:59:42 +0000
Subject: [PATCH] Define _C99 in libstdc++ vxworks/os_defines.h

To request C99 features from old system headers, on which
libstc++ relies since at least c++98. The specific issue that
exposed this was a failure to compile

  libstdc++-v3/src/c++17/floating_to_chars.cc

for VxWorks 6.9 with a batch of errors such as:

  error: 'FP_NAN' was not declared in this scope

The missing definitions are provided by the
system headers with guards on _HAS_C9X, which gets
internally defined when _C99 is.

2021-12-07  Olivier Hainque  <hainque@adacore.com>

libstdc++-v3/

	* config/os/vxworks/os_defines.h: #define _C99.
---
 libstdc++-v3/config/os/vxworks/os_defines.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libstdc++-v3/config/os/vxworks/os_defines.h b/libstdc++-v3/config/os/vxworks/os_defines.h
index 75a68bc605b..78392dec30a 100644
--- a/libstdc++-v3/config/os/vxworks/os_defines.h
+++ b/libstdc++-v3/config/os/vxworks/os_defines.h
@@ -100,4 +100,9 @@
 #undef _NO_CPP_INLINES
 #define _NO_CPP_INLINES 1
 
+// libstdc++ relies on C99 features for virtually all versions of C++,
+// up to at least C++98.
+#undef _C99
+#define _C99 1
+
 #endif // _GLIBCXX_OS_DEFINES
-- 
2.25.1