This is a start at making the libc++ test suite friendlier to the -fnoexceptions flag.  Although this is not a complete solution, it does reduce the number of test failures on OS X from 467 to 128 on OS X when -fno-exceptions is enabled, and does not impact the number of failures at all when -fno-exceptions is not enabled.  The bulk of this code was donated anonymously.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@177824 91177308-0d34-0410-b5e6-96231b3b80d8
Marshall Clow found some divide-by-zero warnings with UBSan in rand's binomial_distribution test.  This eliminates the divide-by-zeros and describes in comments the numerical difficulties the test is having.  Each of the problematic tests are exploring edge cases of the distribution.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@177826 91177308-0d34-0410-b5e6-96231b3b80d8