Fix conversion warnings (#989)

* Fix sign conversion warnings

* Ignore unused local typedefs

* Remove cast reported as useless on GCC

* Remove warning on unused variable

* Enable conversion warning checking for pedantic build

* Fix sign-conversion warnings in headers

test/core-test.cc

@@ -492,7 +492,7 @@ class QString {
 
 inline fmt::basic_string_view<wchar_t> to_string_view(
     const QString &s) FMT_NOEXCEPT {
-  return {reinterpret_cast<const wchar_t *>(s.utf16()),
+  return {s.utf16(),
           static_cast<std::size_t>(s.size())};
 }
 }

test/format-test.cc

@@ -1917,6 +1917,7 @@ TEST(FormatTest, Enum) {
 
 TEST(FormatTest, EnumFormatterUnambiguous) {
   fmt::formatter<TestEnum> f;
+  ASSERT_GE(sizeof(f), 0); // use f to avoid compiler warning
 }
 
 #if FMT_HAS_FEATURE(cxx_strong_enums)