GH-45325: [C++] Improved error message when using clang++ without clang

cpp/cmake_modules/SetupCxxFlags.cmake

@@ -23,6 +23,23 @@ include(CheckCXXSourceCompiles)
 
 message(STATUS "System processor: ${CMAKE_SYSTEM_PROCESSOR}")
 
+if(CMAKE_C_COMPILER_ID STREQUAL "AppleClang" OR CMAKE_C_COMPILER_ID STREQUAL "Clang")
+  set(UsingClang TRUE)
+else()
+  set(UsingClang FALSE)
+endif()
+
+# Check for Clang C++ compiler
+if(CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" OR CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+  set(UsingClangPlusPlus TRUE)
+else()
+  set(UsingClangPlusPlus FALSE)
+endif()
+
+if(${UsingClangPlusPlus} AND NOT ${UsingClang})
+  message(FATAL_ERROR "When using clang++ you must also use clang")
+endif()
+
 if(NOT DEFINED ARROW_CPU_FLAG)
   if(CMAKE_SYSTEM_NAME STREQUAL "Emscripten")
     set(ARROW_CPU_FLAG "emscripten")
@@ -430,14 +447,6 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang" OR CMAKE_CXX_COMPILER_ID STRE
                                                       "Clang")
   # Clang options for all builds
 
-  # Using Clang with ccache causes a bunch of spurious warnings that are
-  # purportedly fixed in the next version of ccache. See the following for details:
-  #
-  #   http://petereisentraut.blogspot.com/2011/05/ccache-and-clang.html
-  #   http://petereisentraut.blogspot.com/2011/09/ccache-and-clang-part-2.html
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Qunused-arguments")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Qunused-arguments")
-
   # Avoid error when an unknown warning flag is passed
   set(CXX_COMMON_FLAGS "${CXX_COMMON_FLAGS} -Wno-unknown-warning-option")
   # Add colors when paired with ninja