This appears to have been how it is upstream for about 10 years. Using
an interface breaks if a file descriptor number is passed directly to
`NewFile`, e.g., `NewFile(3, "fuzz_in")` as used in Go 1.18 fuzzing
code.
readdir is disabled on linux for 386 and arm until syscall.seek is implemented there.
windows is hard, so leaving that for later.
File src/os/dir_other_go115.go can be deleted when we drop support for go 1.15.
Also adds TestReadNonDir, which was helpful while debugging.
On wasi, O_RDWR is a bitwise or of read and write mode.
As a result, the bit test result was incorrect, and rewrote it to read-write mode.
However, the bit tests are not necessary (and upstream Go does not use them).
This passes the flags through directly.
This is necessary for the following:
- to make sure os/exec can be imported
- to make sure internal/testenv can be imported
The internal/testenv package (which imports os/exec) is used by a lot of
tests. By adding support for it, more tests can be run.
This commit adds a bunch of new packages that now pass all tests.
