Ensure NoDefinitions gets initialized only at first use.

Ensure NoDefinitions gets initialized only at first use.

As a global, NoDefinitions could get initialized at program startup,
which happens specifically with Visual Studio. This causes the
progam to abort because its initialization depends on a TLS variable
to be (manually) initialized first. Since there's only one use of
NoDefinitions, it can be moved to that location and since it's at
function scope it only gets constructed at first use.

BUG=swiftshader:7

Change-Id: I30801ad0d0ab380ead33069f174bb78dc1b230ab
Reviewed-on: https://chromium-review.googlesource.com/379955
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Jim Stichnoth <stichnot@chromium.org>