[CMake] Post test in build tree

[Marco Atzeri]

on latest Lapack source there is on "CTestCustom.cmake.in"
the following command

SET(CTEST_CUSTOM_POST_TEST "./lapack_testing.py -s -d TESTING")

but unfortunately as "./lapack_testing.py" is on the source tree
it does not work if the build tree is a different one.

Any suggestion how to modify it ?

Thanks in advance
Marco