Fix even more Clang warnings.

This patch disables shift-sign-overflow warnings for now. It also
fixes most -Wfloat-equal warnings and -Wextra-semi warnings.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@343438 91177308-0d34-0410-b5e6-96231b3b80d8

include/filesystem

@@ -587,7 +587,7 @@ template <class _ECharT>
 typename enable_if<__can_convert_char<_ECharT>::value, bool>::type
 __is_separator(_ECharT __e) {
   return __e == _ECharT('/');
-};
+}
 
 struct _NullSentinal {};