build: Print CMAKE_CXX_COMPILER_ARG1 in summary

When `-DCMAKE_CXX_COMPILER='clang++;-stdlib=libc++;-m32'` is provided,
`-stdlib=libc++ -m32` flags are printed in the summary now.

Author: hebasto

cmake/module/FlagsSummary.cmake

@@ -22,7 +22,8 @@ function(print_flags_per_config config indent_num)
   get_target_interface(definitions "${config}" core_interface COMPILE_DEFINITIONS)
   indent_message("Preprocessor defined macros ..........." "${definitions}" ${indent_num})
 
-  string(STRIP "${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${config_uppercase}}" combined_cxx_flags)
+  string(STRIP "${CMAKE_CXX_COMPILER_ARG1} ${CMAKE_CXX_FLAGS}" combined_cxx_flags)
+  string(STRIP "${combined_cxx_flags} ${CMAKE_CXX_FLAGS_${config_uppercase}}" combined_cxx_flags)
   string(STRIP "${combined_cxx_flags} ${CMAKE_CXX${CMAKE_CXX_STANDARD}_STANDARD_COMPILE_OPTION}" combined_cxx_flags)
   if(CMAKE_POSITION_INDEPENDENT_CODE)
     string(JOIN " " combined_cxx_flags ${combined_cxx_flags} ${CMAKE_CXX_COMPILE_OPTIONS_PIC})