commit 3215d4f5b3d08e0087a88df9e155c779927ace1a
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Apr 30 20:32:05 2021

    libstdc++: Fix inconsistent feature test macros
    
    The __cpp_lib_constexpr_string and __cpp_lib_semaphore feature test
    macros are not defined consistently in <version> and the relevant header
    for the feature.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/basic_string.h (__cpp_lib_constexpr_string):
            Only define for C++17 and later.
            * include/std/version (__cpp_lib_semaphore): Fix condition
            to match the one in <semaphore>.

diff --git a/libstdc++-v3/include/bits/basic_string.h b/libstdc++-v3/include/bits/basic_string.h
index 41d781c698e..fba7c6f3354 100644
--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -55,7 +55,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if __cplusplus == 201703L
 // Support P0426R1 changes to char_traits in C++17.
 # define __cpp_lib_constexpr_string 201611L
-#else
+#elif __cplusplus > 201703L
 // Also support P1032R1 in C++20 (but not P0980R1 yet).
 # define __cpp_lib_constexpr_string 201811L
 #endif
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 09e67a40d0c..ea0e18a3f9d 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -241,7 +241,7 @@
 #if __cpp_lib_concepts
 # define __cpp_lib_ranges 201911L
 #endif
-#if __cpp_lib_atomic_wait
+#if __cpp_lib_atomic_wait || _GLIBCXX_HAVE_POSIX_SEMAPHORE
 # define __cpp_lib_semaphore 201907L
 #endif
 #define __cpp_lib_shift 201806L