Modernize conversion to bool to the explicit bool conversion operator (library wide). This fixes http://llvm.org/bugs/show_bug.cgi?id=12058.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@151088 91177308-0d34-0410-b5e6-96231b3b80d8

include/system_error

@@ -451,7 +451,7 @@ public:
     string message() const;
 
     _LIBCPP_ALWAYS_INLINE
-    //explicit
+        _LIBCPP_EXPLICIT
         operator bool() const _NOEXCEPT {return __val_ != 0;}
 };
 
@@ -528,7 +528,7 @@ public:
     string message() const;
 
     _LIBCPP_ALWAYS_INLINE
-    //explicit
+        _LIBCPP_EXPLICIT
         operator bool() const _NOEXCEPT {return __val_ != 0;}
 };