CONFIG: fixes for MacOS (#2555)

- introduce a FOAM_LD_LIBRARY_PATH variable to shadow
  DYLD_LIBRARY_PATH on MacOS.

  The DYLD_LIBRARY_PATH and LD_LIBRARY_PATH cannot be modified via sub
  shells etc when SIP is active. This helps circumvent these
  restrictions, which is obviously a hack, but seems to be required.

COMP: disable -ftrapping-math in geompack for MacOS

bin/tools/change-sitedir.sh

@@ -49,8 +49,8 @@ then
     foamClean="$WM_PROJECT_DIR/bin/foamCleanPath"
     if [ -x "$foamClean" ]
     then
-        cleaned=$($foamClean "$PATH" "$foamOldDirs") && PATH="$cleaned"
-        cleaned=$($foamClean "$LD_LIBRARY_PATH" "$foamOldDirs") \
+        cleaned=$($foamClean -env=PATH "$foamOldDirs") && PATH="$cleaned"
+        cleaned=$($foamClean -env=LD_LIBRARY_PATH "$foamOldDirs") \
             && LD_LIBRARY_PATH="$cleaned"
     fi