test-periodic: build with same C++ compiler as ROOT
test-periodic: build with same C++ compiler as ROOT

If not built with the same compiler, CMAKE_CXX_FLAGS may contain
flags not known by the default compiler, which will make the test
fail. In particular using Ninja + Clang on Linux makes this test
fail with the error below without this patch.

c++: error: unrecognized command line option ‘-fcolor-diagnostics’
ninja: build stopped: subcommand failed.

karies/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,karies/root,karies/root,karies/root,karies/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,olifre/root,olifre/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,karies/root,olifre/root,olifre/root,karies/root