Chromium's memory sanitizer doesn't work with JIT compiled code, so
we have to skip blitReactor when using MSAN, otherwise most uses of
glReadPixels() will cause MSAN to detect a false use-of-uninitialized-value,
since it doesn't instrument the inside of JIT compiled code.

Bug chromium:848035 chromium:860533

Change-Id: Idfa194ce0fcd41eb7acf7868cbcebfc04d598f5b
Reviewed-on: https://swiftshader-review.googlesource.com/19808Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>