Fix Windows try_lock implementation

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@292011 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/mutex.cpp b/src/mutex.cpp
index 9397ae7..338b79f 100644
--- a/src/mutex.cpp
+++ b/src/mutex.cpp
@@ -37,7 +37,7 @@
 bool
 mutex::try_lock() _NOEXCEPT
 {
-    return __libcpp_mutex_trylock(&__m_) == 0;
+    return __libcpp_mutex_trylock(&__m_);
 }
 
 void
@@ -83,7 +83,7 @@
 bool
 recursive_mutex::try_lock() _NOEXCEPT
 {
-    return __libcpp_recursive_mutex_trylock(&__m_) == 0;
+    return __libcpp_recursive_mutex_trylock(&__m_);
 }
 
 // timed_mutex