Add "-no-warn-sample-unuse=true" to work around AutoFDO issue

Autofdo generates profile for an instruction even if there is no debug
information associated with it or no debug information associated with
the function. A bogus offset will be produced in the profile. Add the
flag to suppress Clang from generating error for such cases.

Test: build with ETM profile
Bug: 147844018
Bug: 79161490
Change-Id: I37da1ba3a4962072ccdf01f79fbf2c2b4c77b56b