[libcxx] Use _ftelli64/_fseeki64 on Windows

This allows using the full 64 bit range for file offsets.

This should fix the issue reported downstream at
mstorsjo/llvm-mingw#462.

libcxx/include/fstream

@@ -936,7 +936,11 @@ basic_filebuf<_CharT, _Traits>::seekoff(off_type __off, ios_base::seekdir __way,
   default:
     return pos_type(off_type(-1));
   }
-#    if !_LIBCPP_HAS_OFF_T_FUNCTIONS
+#    if defined(_LIBCPP_MSVCRT_LIKE)
+  if (_fseeki64(__file_, __width > 0 ? __width * __off : 0, __whence))
+    return pos_type(off_type(-1));
+  pos_type __r = _ftelli64(__file_);
+#    elif !_LIBCPP_HAS_OFF_T_FUNCTIONS
   if (fseek(__file_, __width > 0 ? __width * __off : 0, __whence))
     return pos_type(off_type(-1));
   pos_type __r = ftell(__file_);
@@ -954,7 +958,10 @@ typename basic_filebuf<_CharT, _Traits>::pos_type
 basic_filebuf<_CharT, _Traits>::seekpos(pos_type __sp, ios_base::openmode) {
   if (__file_ == nullptr || sync())
     return pos_type(off_type(-1));
-#    if !_LIBCPP_HAS_OFF_T_FUNCTIONS
+#    if defined(_LIBCPP_MSVCRT_LIKE)
+  if (_fseeki64(__file_, __sp, SEEK_SET))
+    return pos_type(off_type(-1));
+#    elif !_LIBCPP_HAS_OFF_T_FUNCTIONS
   if (fseek(__file_, __sp, SEEK_SET))
     return pos_type(off_type(-1));
 #    else

libcxx/test/std/input.output/file.streams/fstreams/ifstream.members/offset_range.pass.cpp

@@ -11,12 +11,6 @@
 // Test that we can seek using offsets larger than 32 bit, and that we can
 // retrieve file offsets larger than 32 bit.
 
-// On MSVC targets, we only use the 32 bit fseek/ftell functions. For MinGW
-// targets, we use fseeko/ftello, but the user needs to define
-// _FILE_OFFSET_BITS=64 to make them 64 bit.
-//
-// XFAIL: target={{.*}}-windows{{.*}}
-
 // On 32 bit Android platforms, off_t is 32 bit by default. By defining
 // _FILE_OFFSET_BITS=64, one gets a 64 bit off_t, but the corresponding
 // 64 bit ftello/fseeko functions are only available since Android API 24 (7.0).