* Add two strlen optimizations:

* Add two strlen optimizations:
    strlen(x) != 0 -> *x != 0
    strlen(x) == 0 -> *x == 0
* Change nested statistics to use style of other LLVM statistics so that
  only the name of the optimization (simplify-libcalls) is used as the
  statistic name, and the description indicates which specific all is
  optimized. Cuts down on some redundancy and saves a few bytes of space.
* Make note of stpcpy optimization that could be done.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21766 91177308-0d34-0410-b5e6-96231b3b80d8