sstring: constructor from C string

The constructor from "const char_type *" wouldn't really work when
char_type != char, because strlen() won't work on such pointers.

It is more convenient to have a constructor from an ordinary const char *
(e.g., a C string literal), and solve the type problem with an ugly cast.

This only makes sense when sizeof(char_type)==1 (i.e., it is char, unsigned
char, or signed char), but I think we make this assumption in other places
as well (e.g., in determining the size we need to allocate).

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>

core/sstring.hh

@@ -105,7 +105,7 @@ public:
             u.external.str[size] = '\0';
         }
     }
-    basic_sstring(const char_type* x) : basic_sstring(x, std::strlen(x)) {}
+    basic_sstring(const char* x) : basic_sstring(reinterpret_cast<const char_type*>(x), std::strlen(x)) {}
     basic_sstring(std::basic_string<char_type>& x) : basic_sstring(x.c_str(), x.size()) {}
     basic_sstring(std::initializer_list<char_type> x) : basic_sstring(x.begin(), x.end() - x.begin()) {}
     basic_sstring(const char_type* b, const char_type* e) : basic_sstring(b, e - b) {}