Add/fix missing WASI functionality to pass libstd tests

This rather large commit adds/fixes missing WASI functionality
in `libstd` needed to pass the `libstd` tests. As such, now by
default tests targeting `wasm32-wasi` target are enabled in
`test/tests.zig` module. However, they can be disabled by passing
the `-Dskip-wasi=true` flag when invoking the `zig build test`
command. When the flag is set to `false`, i.e., when WASI tests are
included, `wasmtime` with `--dir=.` is used as the default testing
command.

Since the majority of `libstd` tests were relying on `fs.cwd()`
call to get current working directory handle wrapped in `Dir`
struct, in order to make the tests WASI-friendly, `fs.cwd()`
call was replaced with `testing.getTestDir()` function which
resolved to either `fs.cwd()` for non-WASI targets, or tries to
fetch the preopen list from the WASI runtime and extract a
preopen for '.' path.

The summary of changes introduced by this commit:
* implement `Dir.makeDir` and `Dir.openDir` targeting WASI
* implement `Dir.deleteFile` and `Dir.deleteDir` targeting WASI
* fix `os.close` and map errors in `unlinkat`
* move WASI-specific `mkdirat` and `unlinkat` from `std.fs.wasi`
  to `std.os` module
* implement `lseek_{SET, CUR, END}` targeting WASI
* implement `futimens` targeting WASI
* implement `ftruncate` targeting WASI
* implement `readv`, `writev`, `pread{v}`, `pwrite{v}` targeting WASI
* make sure ANSI escape codes are _not_ used in stderr or stdout
  in WASI, as WASI always sanitizes stderr, and sanitizes stdout if
  fd is a TTY
* fix specifying WASI rights when opening/creating files/dirs
* tweak `AtomicFile` to be WASI-compatible
* implement `os.renameatWasi` for WASI-compliant `os.renameat` function
* implement sleep() targeting WASI
* fix `process.getEnvMap` targeting WASI

1 files changed, 20 insertions, 0 deletions

diff --git a/test/tests.zig b/test/tests.zig
index d5fdbd74cf..b538818634 100644
--- a/test/tests.zig
+++ b/test/tests.zig
@@ -52,6 +52,15 @@ const test_targets = blk: {
 
         TestTarget{
             .target = .{
+                .cpu_arch = .wasm32,
+                .os_tag = .wasi,
+            },
+            .link_libc = false,
+            .single_threaded = true,
+        },
+
+        TestTarget{
+            .target = .{
                 .cpu_arch = .x86_64,
                 .os_tag = .linux,
                 .abi = .none,
@@ -463,6 +472,7 @@ pub fn addPkgTests(
     skip_single_threaded: bool,
     skip_non_native: bool,
     skip_libc: bool,
+    skip_wasi: bool,
     is_wine_enabled: bool,
     is_qemu_enabled: bool,
     glibc_dir: ?[]const u8,
@@ -473,6 +483,15 @@ pub fn addPkgTests(
         if (skip_non_native and !test_target.target.isNative())
             continue;
 
+        if (skip_wasi) {
+            if (test_target.target.os_tag) |tag| {
+                if (tag == .wasi) {
+                    warn("Skipping {} on wasm32-wasi.\n", .{root_src});
+                    continue;
+                }
+            }
+        }
+
         if (skip_libc and test_target.link_libc)
             continue;
 
@@ -525,6 +544,7 @@ pub fn addPkgTests(
         these_tests.overrideZigLibDir("lib");
         these_tests.enable_wine = is_wine_enabled;
         these_tests.enable_qemu = is_qemu_enabled;
+        these_tests.enable_wasmtime = !skip_wasi;
         these_tests.glibc_multi_install_dir = glibc_dir;
 
         step.dependOn(&these_tests.step);