C++ feature checks: Filter out warnings caused by local configuration

In some environments the linker produces warnings like

    warning: directory not found for option
    warning: object file compiled with -mlong-branch ...

These do not affect the availability of C++ features we're checking,
so filter them out.

Fixes: #17850, #17947

Source/Checks/cm_cxx_features.cmake

@@ -19,6 +19,9 @@ function(cm_check_cxx_feature name)
     string(REGEX REPLACE " +0 Warning\\(s\\)" "" check_output "${check_output}")
     # Filter out warnings caused by user flags.
     string(REGEX REPLACE "[^\n]*warning:[^\n]*-Winvalid-command-line-argument[^\n]*" "" check_output "${check_output}")
+    # Filter out warnings caused by local configuration.
+    string(REGEX REPLACE "[^\n]*warning:[^\n]*directory not found for option[^\n]*" "" check_output "${check_output}")
+    string(REGEX REPLACE "[^\n]*warning:[^\n]*object file compiled with -mlong-branch which is no longer needed[^\n]*" "" check_output "${check_output}")
     # If using the feature causes warnings, treat it as broken/unavailable.
     if(check_output MATCHES "[Ww]arning")
       set(CMake_HAVE_CXX_${FEATURE} OFF CACHE INTERNAL "TRY_COMPILE" FORCE)