[lldb/TestingSupport] Manually disable GTEST_HAS_TR1_TUPLE

Gtest 1.8.0 uses tr1::tuple which is deprecated on MSVC. We have to force it off
to avoid the compiler warnings, which will become errors after switching on C++17
(https://devblogs.microsoft.com/cppblog/c17-feature-removals-and-deprecations).