fix: adjust C++ standard and compiler flags for Apple Clang

Signed-off-by: Dhruv Patel <[email protected]>

Author: idesign0

nav2_mppi_controller/CMakeLists.txt

@@ -1,6 +1,13 @@
 cmake_minimum_required(VERSION 3.5)
 project(nav2_mppi_controller)
 
+if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+# Use C++20 on Apple Clang to support Concepts natively and avoid -fconcepts
+    set(CMAKE_CXX_STANDARD 20)
+    set(CMAKE_CXX_STANDARD_REQUIRED ON)
+    set(CMAKE_CXX_EXTENSIONS OFF)  # Use -std=c++20, not -std=gnu++20
+endif()
+
 find_package(ament_cmake REQUIRED)
 find_package(angles REQUIRED)
 find_package(backward_ros REQUIRED)
@@ -83,7 +90,12 @@ add_library(mppi_critics SHARED
   src/critics/twirling_critic.cpp
   src/critics/velocity_deadband_critic.cpp
 )
-target_compile_options(mppi_critics PUBLIC -fconcepts -O3)
+if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    # Apple Clang: use C++20 and optimization, omit -fconcepts
+    target_compile_options(mppi_critics PUBLIC -O3)
+else()
+    target_compile_options(mppi_critics PUBLIC -fconcepts -O3)
+endif()
 target_include_directories(mppi_critics
   PUBLIC
     "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>"