CMake: set standard in specific toolchain files

As the Mbed OS toolchain file is included by CMake, we need to have enabling language in the main CMake (can be executed
only once). Also providing C/C++ standard set functions per toolchain (we can refactor these to provide common or in util)

Author: 0xc0170

CMakeLists.txt

@@ -21,7 +21,11 @@ include(${MBED_CONFIG_PATH}/mbed_config.cmake)
 include(${MBED_ROOT}/cmake/core.cmake)
 mbed_set_cpu_core_options(mbed-os ${MBED_TOOLCHAIN})
 
-set(CMAKE_TOOLCHAIN_FILE "${MBED_ROOT}/cmake/toolchain.cmake" CACHE INTERNAL "")
+# Set the toolchain file, do not include it as it's included by CMake on system level
+if(NOT CMAKE_TOOLCHAIN_FILE)
+    set(CMAKE_TOOLCHAIN_FILE "${MBED_ROOT}/cmake/toolchain.cmake" CACHE INTERNAL "")
+endif()
+
 include(${MBED_ROOT}/cmake/toolchains/${MBED_TOOLCHAIN}.cmake)
 enable_language(C CXX ASM)
 mbed_set_toolchain_options(mbed-os)

cmake/toolchain.cmake

@@ -40,11 +40,6 @@ elseif (MBED_CPU_CORE STREQUAL Cortex-M7FD)
     set(CMAKE_SYSTEM_PROCESSOR cortex-m7)
 endif()
 
-#include(${MBED_ROOT}/cmake/toolchains/${MBED_TOOLCHAIN}.cmake)
-
-# Project setup
-#enable_language(C CXX ASM)
-
 # Clear toolchains options for all languages as Mbed OS uses
 # different initialisation options (such as for optimization and debug symbols)
 set(CMAKE_C_FLAGS_DEBUG "" CACHE STRING "" FORCE)

cmake/toolchains/ARM.cmake

@@ -19,6 +19,22 @@ if(MBEDIDE)
     set_property(GLOBAL PROPERTY MBED_STUDIO_ARM_COMPILER "--ide=mbed")
 endif()
 
+# Set the language standard to use per target
+function(mbed_set_language_standard target)
+    set_target_properties(${target}
+        PROPERTIES
+            C_STANDARD 11
+            C_STANDARD_REQUIRED YES
+            C_EXTENSIONS YES
+    )
+
+    set_target_properties(${target}
+        PROPERTIES
+            CXX_STANDARD 14
+            CXX_STANDARD_REQUIRED YES
+            CXX_EXTENSIONS YES
+    )
+endfunction()
 
 # Sets toolchain options
 function(mbed_set_toolchain_options target)

cmake/toolchains/GCC_ARM.cmake

@@ -13,6 +13,22 @@ set(CMAKE_CXX_COMPILER "arm-none-eabi-g++")
 set(GCC_ELF2BIN "arm-none-eabi-objcopy")
 set_property(GLOBAL PROPERTY ELF2BIN ${GCC_ELF2BIN})
 
+# Set the language standard to use per target
+function(mbed_set_language_standard target)
+    set_target_properties(${target}
+        PROPERTIES
+            C_STANDARD 11
+            C_STANDARD_REQUIRED YES
+            C_EXTENSIONS YES
+    )
+
+    set_target_properties(${target}
+        PROPERTIES
+            CXX_STANDARD 14
+            CXX_STANDARD_REQUIRED YES
+            CXX_EXTENSIONS YES
+    )
+endfunction()
 
 # Sets toolchain options
 function(mbed_set_toolchain_options target)

cmake/util.cmake

@@ -15,20 +15,3 @@ function(mbed_add_cmake_directory_if_labels PREFIX)
         endif()
     endforeach()
 endfunction()
-
-# Set the language standard to use per target
-function(mbed_set_language_standard target)
-    set_target_properties(${target}
-        PROPERTIES
-            C_STANDARD 11
-            C_STANDARD_REQUIRED YES
-            C_EXTENSIONS YES
-    )
-
-    set_target_properties(${target}
-        PROPERTIES
-            CXX_STANDARD 14
-            CXX_STANDARD_REQUIRED YES
-            CXX_EXTENSIONS YES
-    )
-endfunction()