libc - Disallow an excessively large pattern space

libc - Disallow an excessively large pattern space

* Disallow pattern spaces which would cause intermediate calculations
  to overflow size_t.

* Since the pattern length must be in the hundreds of megabytes to trigger
  the issue on a 32-bit machine (and something insane on a 64-bit machine),
  it is unlikely that any software is at risk.  But still a good idea to
  deal with the case.

CERT: VU#695940