Move the code generation mutex to Reactor.

Generation of the routines for copying surfaces and blitting
were not protected by the same critical section as the renderer.

Change-Id: I10eb386bdeebb04abc999b3313dc2c3b52adc090
Reviewed-on: https://swiftshader-review.googlesource.com/2772
Tested-by: Greg Hartman <ghartman@google.com>
Reviewed-by: Greg Hartman <ghartman@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>