Implement LCM and GCD for C++17. Same code as for Library Fundamentals TS.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@276751 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/numerics/numeric.ops/numeric.ops.lcm/lcm.not_integral1.fail.cpp

@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// <numeric>
+
+// template<class _M, class _N>
+// constexpr common_type_t<_M,_N> lcm(_M __m, _N __n)
+
+// Remarks: If either M or N is not an integer type, the program is ill-formed.
+
+#include <numeric>
+
+
+int main()
+{
+    std::lcm(2.0, 4);
+}