dynamically adjust pattern value

_From [bruen...@google.com](https://code.google.com/u/109494838902877177630/) on April 11, 2012 16:46:36_

particular patterns can be problematic with particular apps. this case
covers monitoring the # of non-error faults and at some threshold changing
the pattern, which requires flushing the whole cache b/c the pattern is
embedded as immeds in cmps. (note that w/ 32-to-64, or stealing a reg in
general, we could avoid the flush by putting the immed in a reg: which is a
shorter instruction too)

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=860_