#1005: cmake: cache compiler checks for warning flags

cmake/turn_on_warnings.cmake

@@ -1,23 +1,22 @@
 include(CheckCXXCompilerFlag)
 
-function(enable_cxx_compiler_flag_if_supported flag)
+function(enable_cxx_compiler_flag_if_supported flag var)
   string(FIND "${CMAKE_CXX_FLAGS}" "${flag}" flag_already_set)
   if(flag_already_set EQUAL -1)
-    check_cxx_compiler_flag("${flag}" flag_supported)
+    check_cxx_compiler_flag("${flag}" ${var})
     if(flag_supported)
       set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${flag}" PARENT_SCOPE)
     endif()
-    unset(flag_supported CACHE)
   endif()
 endfunction()
 
 get_directory_property(hasParent PARENT_DIRECTORY)
 if(NOT hasParent)
-  enable_cxx_compiler_flag_if_supported("-Wall")
-  enable_cxx_compiler_flag_if_supported("-pedantic")
-  enable_cxx_compiler_flag_if_supported("-Wshadow")
-  enable_cxx_compiler_flag_if_supported("-Wno-unknown-pragmas")
-  enable_cxx_compiler_flag_if_supported("-Wsign-compare")
+  enable_cxx_compiler_flag_if_supported("-Wall" VT_WALL_FLAG_SUPPORTED)
+  enable_cxx_compiler_flag_if_supported("-pedantic" VT_PEDANTIC_FLAG_SUPPORTED)
+  enable_cxx_compiler_flag_if_supported("-Wshadow" VT_WSHADOW_FLAG_SUPPORTED)
+  enable_cxx_compiler_flag_if_supported("-Wno-unknown-pragmas" VT_WNO_UNKNOWN_PRAGMAS_FLAG_SUPPORTED)
+  enable_cxx_compiler_flag_if_supported("-Wsign-compare" VT_WSIGN_COMPARE_SUPPORTED)
   # Not really a warning, is still diagnostic related..
-  enable_cxx_compiler_flag_if_supported("-ftemplate-backtrace-limit=100")
+  enable_cxx_compiler_flag_if_supported("-ftemplate-backtrace-limit=100" VT_FTEMPLATE_BACKTRACE_LIMIT_SUPPORTED)
 endif()