Invoke sed in a BSD-sed-compatible way.

Upstream has solved it in a different way, so this patch will not be needed
in later versions of freecad.

https://github.com/FreeCAD/FreeCAD/commit/c44ade6961c39009dee34f61491f27ccf8b81852
--- cMake/FindPySide2Tools.cmake.orig	2019-10-22 11:53:35.000000000 -0500
+++ cMake/FindPySide2Tools.cmake	2019-10-28 21:55:27.000000000 -0500
@@ -42,7 +42,7 @@
         # we follow the tool command with in-place sed.
         ADD_CUSTOM_COMMAND(OUTPUT ${outfile}
           COMMAND "${PYSIDE2UICBINARY}" "${infile}" -o "${outfile}"
-          COMMAND sed -i "/^# /d" "${outfile}"
+          COMMAND sed -i .orig "/^# /d" "${outfile}"
           MAIN_DEPENDENCY "${infile}"
         )
     endif()
@@ -69,7 +69,7 @@
         # we follow the tool command with in-place sed.
         ADD_CUSTOM_COMMAND(OUTPUT "${outfile}"
           COMMAND "${PYSIDE2RCCBINARY}" "${infile}" ${PY_ATTRIBUTE} -o "${outfile}"
-          COMMAND sed -i "/^# /d" "${outfile}"
+          COMMAND sed -i .orig "/^# /d" "${outfile}"
           MAIN_DEPENDENCY "${infile}"
         )
     endif()
--- cMake/FindPySideTools.cmake.orig	2019-10-22 11:53:35.000000000 -0500
+++ cMake/FindPySideTools.cmake	2019-10-28 21:55:21.000000000 -0500
@@ -42,7 +42,7 @@
         # we follow the tool command with in-place sed.
         ADD_CUSTOM_COMMAND(OUTPUT ${outfile}
           COMMAND "${PYSIDEUIC4BINARY}" "${infile}" -o "${outfile}"
-          COMMAND sed -i "/^# /d" "${outfile}"
+          COMMAND sed -i .orig "/^# /d" "${outfile}"
           MAIN_DEPENDENCY "${infile}"
         )
     endif(WIN32)
@@ -74,7 +74,7 @@
         # we follow the tool command with in-place sed.
         ADD_CUSTOM_COMMAND(OUTPUT "${outfile}"
           COMMAND "${PYSIDERCC4BINARY}" "${infile}" ${PY_ATTRIBUTE} -o "${outfile}"
-          COMMAND sed -i "/^# /d" "${outfile}"
+          COMMAND sed -i .orig "/^# /d" "${outfile}"
           MAIN_DEPENDENCY "${infile}"
         )
     endif(WIN32)