[gcc r12-3978] libstdc++: Fix preprocessor check for C++17

[Jonathan Wakely]

https://gcc.gnu.org/g:c5369961fa3a5a319f1cc1469c6afb8b679e4846

commit r12-3978-gc5369961fa3a5a319f1cc1469c6afb8b679e4846
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Sep 30 08:59:21 2021 +0100

    libstdc++: Fix preprocessor check for C++17
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/regex.h (basic_regex::multiline): Fix #if
            condition.

Diff:
---
 libstdc++-v3/include/bits/regex.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h
index ad33ecaa14b..664944b0ef2 100644
--- a/libstdc++-v3/include/bits/regex.h
+++ b/libstdc++-v3/include/bits/regex.h
@@ -424,7 +424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
       static constexpr flag_type awk = regex_constants::awk;
       static constexpr flag_type grep = regex_constants::grep;
       static constexpr flag_type egrep = regex_constants::egrep;
-#if __cplusplus >= 2017
+#if __cplusplus >= 201703L
       static constexpr flag_type multiline = regex_constants::multiline;
 #endif
       ///@}