[Bug libstdc++/126365] New: In correct values for feature test macros when using <version>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126365

            Bug ID: 126365
           Summary: In correct values for feature test macros when using
                    <version>
           Product: gcc
           Version: 16.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lcarreon at bigpond dot net.au
  Target Milestone: ---

It appears that when -std=c++23 is set for the compiler, several feature test
macros have the wrong values when using "#include <version>".  For example,
__cpp_lib_chrono has the value 201907.  According to the C++ compiler support
tables at isocpp.org, gcc has P2592R3 implemented in gcc 16 therefore the
expected value for __cpp_lib_chrono is 202306 as per SD-Feature Test standing
document.  I have looked in bits/version.h and I think the reason why is
because of this line:

  # if (__cplusplus >  202302L) && _GLIBCXX_USE_CXX11_ABI && _GLIBCXX_HOSTED

Imo, the ">" sign should be ">=" because the value of __cplusplus when
-std=c++23 is 202302 thus the above test would be false instead of true.

It seems several C++23 tests in this header file are all incorrect because of
">" instead of ">=".