[gcc r11-8436] doc: Update description of __GXX_EXPERIMENTAL_CXX0X__

[gcc r11-8436] doc: Update description of __GXX_EXPERIMENTAL_CXX0X__

[Jonathan Wakely]

https://gcc.gnu.org/g:b02eef7b28890f58efb922615811901cbc755c50

commit r11-8436-gb02eef7b28890f58efb922615811901cbc755c50
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed May 19 11:11:11 2021 +0100

    doc: Update description of __GXX_EXPERIMENTAL_CXX0X__
    
    This macro has been obsolete for years, and C++0x features are no longer
    experimental or liable to be removed.
    
    gcc/ChangeLog:
    
            * doc/cpp.texi (Common Predefined Macros): Update documentation
            for the __GXX_EXPERIMENTAL_CXX0X__ macro.
    
    (cherry picked from commit 9b50282b0dcf79d3141979e466465a23d1816166)

Diff:
---
 gcc/doc/cpp.texi | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi
index 2c109bbc5bd..4b065b651b0 100644
--- a/gcc/doc/cpp.texi
+++ b/gcc/doc/cpp.texi
@@ -2312,11 +2312,13 @@ mechanism based on @code{setjmp} and @code{longjmp} for exception
 handling.
 
 @item __GXX_EXPERIMENTAL_CXX0X__
-This macro is defined when compiling a C++ source file with the option
-@option{-std=c++0x} or @option{-std=gnu++0x}. It indicates that some
-features likely to be included in C++0x are available. Note that these
-features are experimental, and may change or be removed in future
-versions of GCC.
+This macro is defined when compiling a C++ source file with C++11 features
+enabled, i.e., for all C++ language dialects except @option{-std=c++98}
+and @option{-std=gnu++98}. This macro is obsolete, but can be used to
+detect experimental C++0x features in very old versions of GCC. Since
+GCC 4.7.0 the @code{__cplusplus} macro is defined correctly, so most
+code should test @code{__cplusplus >= 201103L} instead of using this
+macro.
 
 @item __GXX_WEAK__
 This macro is defined when compiling a C++ source file.  It has the