...so ASan builds do not complain about ODR violations due to multiple instances
of vtable for testtools::bridgetest::CurrentContextChecker after
a53808c0 "loplugin:dllprivate" removed the
SAL_DLLPRIVATE from class CurrentContextChecker (which apparently /did/ have an
impact with -fvisibility-ms-compat, as used by Linux Clang ASan/UBSan builds).

Change-Id: Ifb1ba1819f7ea989300f4696d44f9599a1436563