noexcept applied to <random>.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@160579 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/random.cpp b/src/random.cpp
index 6140b74..97a40c5 100644
--- a/src/random.cpp
+++ b/src/random.cpp
@@ -40,7 +40,7 @@
 }
 
 double
-random_device::entropy() const
+random_device::entropy() const _NOEXCEPT
 {
     return 0;
 }