[libFuzzer] Use std::discrete_distribution for input selection.
[libFuzzer] Use std::discrete_distribution for input selection.

Summary:
Since we're casting from double to size_t during input selection, we
really want a discrete distribution over size_t rather than a piecewise
distribution over doubles.

Reviewers: kcc

Reviewed By: kcc

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D50356

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@339973 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt