Constrain fill_n -> memset operations to include implicit convertibility to unsigned char.  This fixes http://llvm.org/bugs/show_bug.cgi?id=16764.  Also a drive-by fix on a chrono test suite bug.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@187552 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/algorithm b/include/algorithm
index 19d016f..119fbbb 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -2012,6 +2012,7 @@
    return _VSTD::__fill_n(__first, __n, __value_, integral_constant<bool,
                                               is_pointer<_OutputIterator>::value &&
                                               is_trivially_assignable<typename remove_pointer<_OutputIterator>::type, _Tp>::value &&
+                                              is_convertible<_Tp, unsigned char>::value &&
                                               sizeof(typename remove_pointer<_OutputIterator>::type) == 1>());
 }