[libcxx] [test] Avoid narrowing conversions in quoted.pass.cpp.

[STL_MSFT]

Summary

Avoid narrowing conversions in quoted.pass.cpp.

According to the Standard, when char has a signed range and wchar_t has an unsigned range, brace-init has to reject the potentially narrowing conversion.

Fixes MSVC error C2397 "conversion from 'char' to 'wchar_t' requires a narrowing conversion".

[EricWF]

It seems like this has the possibility to lose some useful diagnostics if a narrowing conversion actually occurs.
However I'm OK with the change.

[EricWF]

r273818.

test/std/input.output/iostream.format/quoted.manip/quoted.pass.cpp

void round_trip_ws ( const CharT *p ) {
     ss >> std::quoted(s);
     assert ( s == p );
     assert ( skippingws == is_skipws ( ss ));
     }
 
 template <class CharT, class Traits = std::char_traits<CharT>>
 void round_trip_d ( const CharT *p, char delim ) {
     std::basic_stringstream<CharT, Traits> ss;
-    CharT d{delim};
+    CharT d(delim);
 
     ss << std::quoted(p, d);
     std::basic_string<CharT, Traits> s;
     ss >> std::quoted(s, d);
     assert ( s == p );
     }
 
 template <class CharT, class Traits = std::char_traits<CharT>>
 void round_trip_e ( const CharT *p, char escape ) {
     std::basic_stringstream<CharT, Traits> ss;
-    CharT e{escape};
+    CharT e(escape);
 
     ss << std::quoted(p, CharT('"'), e );
     std::basic_string<CharT, Traits> s;
     ss >> std::quoted(s, CharT('"'), e );
     assert ( s == p );
     }
 
 
 template <class CharT, class Traits = std::char_traits<CharT>>
 std::basic_string<CharT, Traits> quote ( const CharT *p, char delim='"', char escape='\\' ) {
     std::basic_stringstream<CharT, Traits> ss;
-    CharT d{delim};
-    CharT e{escape};
+    CharT d(delim);
+    CharT e(escape);
     ss << std::quoted(p, d, e);
     std::basic_string<CharT, Traits> s;
     ss >> s;    // no quote
     return s;
 }
 
 template <class CharT, class Traits = std::char_traits<CharT>>
 std::basic_string<CharT, Traits> unquote ( const CharT *p, char delim='"', char escape='\\' ) {
     std::basic_stringstream<CharT, Traits> ss;
     ss << p;
 
-    CharT d{delim};
-    CharT e{escape};
+    CharT d(delim);
+    CharT e(escape);
     std::basic_string<CharT, Traits> s;
     ss >> std::quoted(s, d, e);
     return s;
 }
 
 void test_padding () {
     {
     std::stringstream ss;