os: implement os.(*File).Truncate and os.Truncate

[achille-roussel]

This PR adds an implementation of os.(*File).Truncate and os.Truncate. The implementation is based on libc's truncate and ftruncate functions. I ported the tests from the Go standard library as well.

[achille-roussel]

I'm investigating the issue reported by Linux / assert-test-linux; make test fails with:

--- FAIL: TestTest (0.00s)
    --- FAIL: TestTest/WASM (0.00s)
        --- FAIL: TestTest/WASM/Pass (0.30s)
            main_test.go:521: FAIL	github.com/tinygo-org/tinygo/tests/testing/pass	0.000s
            main_test.go:430: test error: could not compile: /home/achille_roussel/go/src/github.com/achille-roussel/tinygo/src/os/file_posix.go:19:17: Truncate not declared by package syscall
            main_test.go:433: test failed
        --- FAIL: TestTest/WASM/Fail (0.30s)
            main_test.go:521: FAIL	github.com/tinygo-org/tinygo/tests/testing/fail	0.000s
            main_test.go:451: test error: could not compile: /home/achille_roussel/go/src/github.com/achille-roussel/tinygo/src/os/file_posix.go:19:17: Truncate not declared by package syscall

Tho testing the os package directly seems to work:

$ ./build/tinygo test -target=wasi os
ok  	os	0.024s

Trying to figure out what is it that I don't understand about the difference between these two tests.

[dgryski]

I believe on when building for Linux we use upstream's syscall package, but on other platforms we use the tinygo/src/syscall. That could lead to some of the issues you're seeing.

Maybe also a caching issue?

[aykevl]

Tho testing the os package directly seems to work:

syscall_libc.go is only for WASI, not for js/wasm. Try -target=wasm to reproduce this locally.

[achille-roussel]

I'm going to close this PR since tinygo has integrated the Go 1.21 changes where os.(*File).Truncate is implemented.