CUDA, CXX: Remove HAS_FULL_SUPPORT for C++17 and 20

CMake has no features for C++ versions past 14 and it seems unlikely we'd want
to add any.
Remove the related code.

Modules/Compiler/CMakeCommonCompilerMacros.cmake

@@ -94,20 +94,10 @@ endmacro()
 macro(cmake_record_cxx_compile_features)
   set(_result 0)
   if(_result EQUAL 0 AND DEFINED CMAKE_CXX20_STANDARD_COMPILE_OPTION)
-    if(CMAKE_CXX20_STANDARD__HAS_FULL_SUPPORT)
-      _has_compiler_features_cxx(20)
-    else()
-      _record_compiler_features_cxx(20)
-    endif()
-    unset(CMAKE_CXX20_STANDARD__HAS_FULL_SUPPORT)
+    _has_compiler_features_cxx(20)
   endif()
   if(_result EQUAL 0 AND DEFINED CMAKE_CXX17_STANDARD_COMPILE_OPTION)
-    if(CMAKE_CXX17_STANDARD__HAS_FULL_SUPPORT)
-      _has_compiler_features_cxx(17)
-    else()
-      _record_compiler_features_cxx(17)
-    endif()
-    unset(CMAKE_CXX17_STANDARD__HAS_FULL_SUPPORT)
+    _has_compiler_features_cxx(17)
   endif()
   if(_result EQUAL 0 AND DEFINED CMAKE_CXX14_STANDARD_COMPILE_OPTION)
     if(CMAKE_CXX14_STANDARD__HAS_FULL_SUPPORT)
@@ -138,20 +128,10 @@ endmacro()
 macro(cmake_record_cuda_compile_features)
   set(_result 0)
   if(_result EQUAL 0 AND DEFINED CMAKE_CUDA20_STANDARD_COMPILE_OPTION)
-    if(CMAKE_CUDA20_STANDARD__HAS_FULL_SUPPORT)
-      _has_compiler_features_cuda(20)
-    else()
-      _record_compiler_features_cuda(20)
-    endif()
-    unset(CMAKE_CUDA20_STANDARD__HAS_FULL_SUPPORT)
+    _has_compiler_features_cuda(20)
   endif()
   if(_result EQUAL 0 AND DEFINED CMAKE_CUDA17_STANDARD_COMPILE_OPTION)
-    if(CMAKE_CUDA17_STANDARD__HAS_FULL_SUPPORT)
-      _has_compiler_features_cuda(17)
-    else()
-      _record_compiler_features_cuda(17)
-    endif()
-    unset(CMAKE_CUDA17_STANDARD__HAS_FULL_SUPPORT)
+    _has_compiler_features_cuda(17)
   endif()
   if(_result EQUAL 0 AND DEFINED CMAKE_CUDA14_STANDARD_COMPILE_OPTION)
     if(CMAKE_CUDA14_STANDARD__HAS_FULL_SUPPORT)

Modules/Compiler/Clang.cmake

@@ -155,10 +155,6 @@ macro(__compiler_clang_cxx_standards lang)
       set(CMAKE_${lang}17_EXTENSION_COMPILE_OPTION "-std=gnu++1z")
     endif()
 
-    if(NOT CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 6.0)
-      set(CMAKE_${lang}17_STANDARD__HAS_FULL_SUPPORT ON)
-    endif()
-
     if(NOT CMAKE_${lang}_COMPILER_VERSION VERSION_LESS 11.0)
       set(CMAKE_${lang}20_STANDARD_COMPILE_OPTION "-std=c++20")
       set(CMAKE_${lang}20_EXTENSION_COMPILE_OPTION "-std=gnu++20")
@@ -180,8 +176,6 @@ macro(__compiler_clang_cxx_standards lang)
       # This clang++ is missing some features because of MSVC compatibility.
       unset(CMAKE_${lang}11_STANDARD__HAS_FULL_SUPPORT)
       unset(CMAKE_${lang}14_STANDARD__HAS_FULL_SUPPORT)
-      unset(CMAKE_${lang}17_STANDARD__HAS_FULL_SUPPORT)
-      unset(CMAKE_${lang}20_STANDARD__HAS_FULL_SUPPORT)
     endif()
 
     __compiler_check_default_language_standard(${lang} 2.1 98)

Modules/Compiler/PGI-CXX.cmake

@@ -18,7 +18,6 @@ if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 12.10)
       if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 17.1)
         set(CMAKE_CXX17_STANDARD_COMPILE_OPTION  --c++17)
         set(CMAKE_CXX17_EXTENSION_COMPILE_OPTION --c++17 --gnu_extensions)
-        set(CMAKE_CXX17_STANDARD__HAS_FULL_SUPPORT ON)
       endif()
     endif()
   endif()