[experiment] add alternative wasm sqlite3 implementation available via build-tag (#2863)

This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).

vendor/github.com/ncruces/go-sqlite3/vfs/os_unix_lock.go

@@ -0,0 +1,106 @@
+//go:build (linux || darwin || freebsd || openbsd || netbsd || dragonfly || illumos || sqlite3_flock) && !sqlite3_nosys
+
+package vfs
+
+import (
+	"os"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+func osGetSharedLock(file *os.File) _ErrorCode {
+	// Test the PENDING lock before acquiring a new SHARED lock.
+	if lock, _ := osGetLock(file, _PENDING_BYTE, 1); lock == unix.F_WRLCK {
+		return _BUSY
+	}
+	// Acquire the SHARED lock.
+	return osReadLock(file, _SHARED_FIRST, _SHARED_SIZE, 0)
+}
+
+func osGetReservedLock(file *os.File) _ErrorCode {
+	// Acquire the RESERVED lock.
+	return osWriteLock(file, _RESERVED_BYTE, 1, 0)
+}
+
+func osGetPendingLock(file *os.File, block bool) _ErrorCode {
+	var timeout time.Duration
+	if block {
+		timeout = -1
+	}
+	// Acquire the PENDING lock.
+	return osWriteLock(file, _PENDING_BYTE, 1, timeout)
+}
+
+func osGetExclusiveLock(file *os.File, wait bool) _ErrorCode {
+	var timeout time.Duration
+	if wait {
+		timeout = time.Millisecond
+	}
+	// Acquire the EXCLUSIVE lock.
+	return osWriteLock(file, _SHARED_FIRST, _SHARED_SIZE, timeout)
+}
+
+func osDowngradeLock(file *os.File, state LockLevel) _ErrorCode {
+	if state >= LOCK_EXCLUSIVE {
+		// Downgrade to a SHARED lock.
+		if rc := osReadLock(file, _SHARED_FIRST, _SHARED_SIZE, 0); rc != _OK {
+			// In theory, the downgrade to a SHARED cannot fail because another
+			// process is holding an incompatible lock. If it does, this
+			// indicates that the other process is not following the locking
+			// protocol. If this happens, return _IOERR_RDLOCK. Returning
+			// BUSY would confuse the upper layer.
+			return _IOERR_RDLOCK
+		}
+	}
+	// Release the PENDING and RESERVED locks.
+	return osUnlock(file, _PENDING_BYTE, 2)
+}
+
+func osReleaseLock(file *os.File, _ LockLevel) _ErrorCode {
+	// Release all locks.
+	return osUnlock(file, 0, 0)
+}
+
+func osCheckReservedLock(file *os.File) (bool, _ErrorCode) {
+	// Test the RESERVED lock.
+	lock, rc := osGetLock(file, _RESERVED_BYTE, 1)
+	return lock == unix.F_WRLCK, rc
+}
+
+func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
+	lock := unix.Flock_t{
+		Type:  unix.F_WRLCK,
+		Start: start,
+		Len:   len,
+	}
+	if unix.FcntlFlock(file.Fd(), unix.F_GETLK, &lock) != nil {
+		return 0, _IOERR_CHECKRESERVEDLOCK
+	}
+	return lock.Type, _OK
+}
+
+func osLockErrorCode(err error, def _ErrorCode) _ErrorCode {
+	if err == nil {
+		return _OK
+	}
+	if errno, ok := err.(unix.Errno); ok {
+		switch errno {
+		case
+			unix.EACCES,
+			unix.EAGAIN,
+			unix.EBUSY,
+			unix.EINTR,
+			unix.ENOLCK,
+			unix.EDEADLK,
+			unix.ETIMEDOUT:
+			return _BUSY
+		case unix.EPERM:
+			return _PERM
+		}
+		if errno == unix.EWOULDBLOCK && unix.EWOULDBLOCK != unix.EAGAIN {
+			return _BUSY
+		}
+	}
+	return def
+}