[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/tetratelabs/wazero/internal/sysfs/poll_linux.go

@@ -0,0 +1,59 @@
+//go:build !tinygo
+
+package sysfs
+
+import (
+	"syscall"
+	"time"
+	"unsafe"
+
+	"github.com/tetratelabs/wazero/experimental/sys"
+)
+
+// pollFd is the struct to query for file descriptor events using poll.
+type pollFd struct {
+	// fd is the file descriptor.
+	fd int32
+	// events is a bitmap containing the requested events.
+	events int16
+	// revents is a bitmap containing the returned events.
+	revents int16
+}
+
+// newPollFd is a constructor for pollFd that abstracts the platform-specific type of file descriptors.
+func newPollFd(fd uintptr, events, revents int16) pollFd {
+	return pollFd{fd: int32(fd), events: events, revents: revents}
+}
+
+// _POLLIN subscribes a notification when any readable data is available.
+const _POLLIN = 0x0001
+
+// _poll implements poll on Linux via ppoll.
+func _poll(fds []pollFd, timeoutMillis int32) (n int, errno sys.Errno) {
+	var ts syscall.Timespec
+	if timeoutMillis >= 0 {
+		ts = syscall.NsecToTimespec(int64(time.Duration(timeoutMillis) * time.Millisecond))
+	}
+	return ppoll(fds, &ts)
+}
+
+// ppoll is a poll variant that allows to subscribe to a mask of signals.
+// However, we do not need such mask, so the corresponding argument is always nil.
+func ppoll(fds []pollFd, timespec *syscall.Timespec) (n int, err sys.Errno) {
+	var fdptr *pollFd
+	nfd := len(fds)
+	if nfd != 0 {
+		fdptr = &fds[0]
+	}
+
+	n1, _, errno := syscall.Syscall6(
+		uintptr(syscall.SYS_PPOLL),
+		uintptr(unsafe.Pointer(fdptr)),
+		uintptr(nfd),
+		uintptr(unsafe.Pointer(timespec)),
+		uintptr(unsafe.Pointer(nil)), // sigmask is currently always ignored
+		uintptr(unsafe.Pointer(nil)),
+		uintptr(unsafe.Pointer(nil)))
+
+	return int(n1), sys.UnwrapOSError(errno)
+}