Increase max identifier length from 64 to 128

To allow compiling updated winapi headers which contain at least one
identifier with 68 chars:

GUID_PROCESSOR_CORE_PARKING_OVER_UTILIZATION_HISTORY_DECREASE_FACTOR

It shouldn't cause any problems to increase this limit besides a tiny
increase in the compiler's total memory usage, since it's only used with
static strings or the symb.namepool which, however, assigns ids into
multiple "length categories" and allocates the best fit, as opposed to
allocating the maxlen everytime.