Make language std configurable. (#75519)

RocksDB 7 starts to use C++17 in header.
We should make this configurable, in case user needs higher std version.

List of files to changed is found by `git grep 'CMAKE_[^_]*_STANDARD'`.
Doc string is from CMake code.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75519
Approved by: https://github.com/malfet

CMakeLists.txt

@@ -37,8 +37,8 @@ if(env_cxx_standard GREATER -1)
       WARNING "C++ standard version definition detected in environment variable."
       "PyTorch requires -std=c++14. Please remove -std=c++ settings in your environment.")
 endif()
-set(CMAKE_CXX_STANDARD 14)
-set(CMAKE_C_STANDARD 11)
+set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
+set(CMAKE_C_STANDARD   11 CACHE STRING "The C standard whose features are requested to build this target.")
 
 if(DEFINED GLIBCXX_USE_CXX11_ABI)
   if(${GLIBCXX_USE_CXX11_ABI} EQUAL 1)

android/pytorch_android/CMakeLists.txt

@@ -14,7 +14,7 @@ endif()
 
 include(GNUInstallDirs)
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
 set(CMAKE_VERBOSE_MAKEFILE ON)
 message(STATUS "ANDROID_STL:${ANDROID_STL}")
 

android/pytorch_android_torchvision/CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.4.1)
 project(pytorch_vision_jni CXX)
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
 set(CMAKE_VERBOSE_MAKEFILE ON)
 
 set(pytorch_vision_cpp_DIR ${CMAKE_CURRENT_LIST_DIR}/src/main/cpp)

android/test_app/app/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.4.1)
 set(PROJECT_NAME pytorch_testapp_jni)
 project(${PROJECT_NAME} CXX)
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
 set(CMAKE_VERBOSE_MAKEFILE ON)
 
 set(build_DIR ${CMAKE_SOURCE_DIR}/build)

aten/src/ATen/nnapi/CMakeLists.txt

@@ -3,7 +3,7 @@ if(PYTORCH_NNAPI_STANDALONE)
   cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
   project(pytorch_nnapi)
 
-  set(CMAKE_CXX_STANDARD 14)
+  set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
   find_package(Torch REQUIRED)
 
   set(NNAPI_SRCS

c10/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
 project(c10 CXX)
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
 set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
 
 # Main build file for the C10 library.

cmake/Dependencies.cmake

@@ -1654,14 +1654,14 @@ if(NOT INTERN_BUILD_MOBILE)
     if(CMAKE_VERSION VERSION_LESS "3.1")
       set(CMAKE_C_FLAGS "-std=c11 ${CMAKE_C_FLAGS}")
     else()
-      set(CMAKE_C_STANDARD 11)
+      set(CMAKE_C_STANDARD 11 CACHE STRING "The C standard whose features are requested to build this target.")
     endif()
   endif()
 
   string(APPEND CMAKE_CUDA_FLAGS " -Wno-deprecated-gpu-targets --expt-extended-lambda")
 
   if(NOT CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-    set(CMAKE_CXX_STANDARD 14)
+    set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
   endif()
 
   # use cub in a safe manner, see:

test/mobile/custom_build/CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.1)
 
 project(custom_build_project)
 
-set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
 
 # Find torch library
 find_package(Torch REQUIRED)

torch/lib/libshm/CMakeLists.txt

@@ -19,7 +19,7 @@ endif(MSVC)
 if(CMAKE_VERSION VERSION_LESS "3.1")
   set(CMAKE_CXX_FLAGS "-std=c++14 ${CMAKE_CXX_FLAGS}")
 else()
-  set(CMAKE_CXX_STANDARD 14)
+  set(CMAKE_CXX_STANDARD 14 CACHE STRING "The C++ standard whose features are requested to build this target.")
 endif()
 
 add_library(shm SHARED core.cpp)