Fix memory leak when aborting routine generation.

Fix memory leak when aborting routine generation.

The blitter aborts generating a Reactor routine when a less common
format is being used (causing fallback to statically compiled code). But
the intermediate Reactor and Subzero structures were not being freed. It
is fixed by deleting the global routine when the Function<> goes out of
scope and it hasn't been acquired yet.

Bug chromium:732691

Change-Id: I4904a467454e8e8d2ff0dbf64545823c9fd15802
Reviewed-on: https://swiftshader-review.googlesource.com/10408
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>