posix/except: add templated error_code

posix/except.cpp

@@ -29,7 +29,6 @@ using util::posix::error;
 ///
 /// The error value MUST be an error at construction time.
 error::error (int _code):
-    std::runtime_error (::strerror (_code)),
     m_code (_code)
 {
     CHECK_NEQ (_code, 0);

posix/except.hpp

@@ -25,7 +25,7 @@ namespace util::posix {
     ///
     /// Ideally this would be named `errno' but that symbol is permitted to
     /// be a macro and significantly complicates symbol resolution either way.
-    class error : public std::runtime_error {
+    class error : public std::exception {
     public:
         explicit error (int code);
         error ();
@@ -52,6 +52,15 @@ namespace util::posix {
     };
 
 
+    template <int CodeV>
+    struct error_code : public error {
+        error_code ():
+            error (CodeV)
+        { ; }
+    };
+
+
+
     class eai : public std::runtime_error {
     public:
         explicit eai (int code);