[libc++] Update our documentation on the supported compilers (llvm#165684)

Author: philnik777

libcxx/docs/index.rst

@@ -132,7 +132,7 @@ velocity, libc++ drops support for older compilers as newer ones are released.
 ============ =================== ========================== =====================
 Compiler     Versions            Restrictions               Support policy
 ============ =================== ========================== =====================
-Clang        19, 20, 21-git                                 latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
+Clang        20, 21, 22-git                                 latest two stable releases per `LLVM's release page <https://releases.llvm.org>`_ and the development version
 AppleClang   26.0                                           latest stable release per `Xcode's release page <https://developer.apple.com/documentation/xcode-release-notes>`_
 Open XL      17.1.3 (AIX)                                   latest stable release per `Open XL's documentation page <https://www.ibm.com/docs/en/openxl-c-and-cpp-aix>`_
 GCC          15                  In C++11 or later only     latest stable release per `GCC's release page <https://gcc.gnu.org/releases.html>`_

libcxx/include/__configuration/compiler.h

@@ -33,16 +33,16 @@
 // Warn if a compiler version is used that is not supported anymore
 // LLVM RELEASE Update the minimum compiler versions
 #  if defined(_LIBCPP_CLANG_VER)
-#    if _LIBCPP_CLANG_VER < 1900
-#      warning "Libc++ only supports Clang 19 and later"
+#    if _LIBCPP_CLANG_VER < 2001
+#      warning "Libc++ only supports Clang 20 and later"
 #    endif
 #  elif defined(_LIBCPP_APPLE_CLANG_VER)
-#    if _LIBCPP_APPLE_CLANG_VER < 1600
-#      warning "Libc++ only supports AppleClang 15 and later"
+#    if _LIBCPP_APPLE_CLANG_VER < 1700
+#      warning "Libc++ only supports AppleClang 26 and later"
 #    endif
 #  elif defined(_LIBCPP_GCC_VER)
-#    if _LIBCPP_GCC_VER < 1400
-#      warning "Libc++ only supports GCC 14 and later"
+#    if _LIBCPP_GCC_VER < 1500
+#      warning "Libc++ only supports GCC 15 and later"
 #    endif
 #  endif