NVHPC: Support nvfortran versions that don't support isystem

Fixes: #25019

Modules/Compiler/NVHPC-Fortran.cmake

@@ -1,3 +1,7 @@
 include(Compiler/PGI-Fortran)
 include(Compiler/NVHPC)
 __compiler_nvhpc(Fortran)
+if(CMAKE_Fortran_COMPILER_VERSION VERSION_LESS 21.7)
+  # Before NVHPC 21.7 nvfortran didn't support isystem
+  unset(CMAKE_INCLUDE_SYSTEM_FLAG_Fortran)
+endif()

Tests/RunCMake/CMakeLists.txt

@@ -452,7 +452,7 @@ add_RunCMake_test(add_custom_target)
 add_RunCMake_test(add_dependencies)
 add_RunCMake_test(add_executable)
 add_RunCMake_test(add_library)
-add_RunCMake_test(add_subdirectory)
+add_RunCMake_test(add_subdirectory -DCMAKE_Fortran_COMPILER=${CMAKE_Fortran_COMPILER})
 add_RunCMake_test(add_test)
 add_RunCMake_test(build_command)
 add_executable(exit_code exit_code.c)

Tests/RunCMake/add_subdirectory/RunCMakeTest.cmake

@@ -3,7 +3,9 @@ include(RunCMake)
 run_cmake(DoesNotExist)
 run_cmake(Missing)
 run_cmake(Function)
+set(RunCMake_TEST_OPTIONS -DCMAKE_Fortran_COMPILER=${CMAKE_Fortran_COMPILER})
 run_cmake(System)
+unset(RunCMake_TEST_OPTIONS)
 
 macro(run_cmake_install case)
   set(RunCMake_TEST_BINARY_DIR ${RunCMake_BINARY_DIR}/${case}-build)

Tests/RunCMake/add_subdirectory/System.cmake

@@ -1,4 +1,7 @@
 enable_language(CXX)
+if(CMAKE_Fortran_COMPILER)
+  enable_language(Fortran)
+endif()
 
 add_subdirectory(System SYSTEM)
 

Tests/RunCMake/add_subdirectory/System/CMakeLists.txt

@@ -4,6 +4,11 @@ add_subdirectory(SubSub1 SYSTEM)
 add_subdirectory(SubSub2)
 
 add_library(bar STATIC bar.cpp)
+if(CMAKE_Fortran_COMPILER)
+  target_sources(bar PRIVATE zap.f)
+endif()
+# Verify CMAKE_INCLUDE_SYSTEM_FLAG_<LANG> works
+target_link_libraries(bar PRIVATE subsub1bar)
 
 add_library(foo STATIC foo.cpp)
 set_target_properties(foo PROPERTIES SYSTEM OFF)

Tests/RunCMake/add_subdirectory/System/SubSub1/CMakeLists.txt

@@ -1,4 +1,5 @@
 add_library(subsub1bar STATIC bar.cpp)
+target_include_directories(subsub1bar PUBLIC ${CMAKE_CURRENT_BINARY_DIR})
 
 add_library(subsub1foo STATIC foo.cpp)
 set_target_properties(subsub1foo PROPERTIES SYSTEM OFF)