On 32-bit targets any values over 4GB would wrap and produce the wrong
result.
PR libstdc++/85632 use uintmax_t for arithmetic
* src/filesystem/ops.cc (experimental::filesystem::space): Perform
arithmetic in result type.
* src/filesystem/std-ops.cc (filesystem::space): Likewise.
* testsuite/27_io/filesystem/operations/space.cc: Check total capacity
is greater than free space.
* testsuite/experimental/filesystem/operations/space.cc: New.
From-SVN: r259901
