[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_darwin.go

@@ -0,0 +1,55 @@
+package sysfs
+
+import (
+	"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 Darwin via the corresponding libc function.
+func _poll(fds []pollFd, timeoutMillis int32) (n int, errno sys.Errno) {
+	var fdptr *pollFd
+	nfds := len(fds)
+	if nfds > 0 {
+		fdptr = &fds[0]
+	}
+	n1, _, err := syscall_syscall6(
+		libc_poll_trampoline_addr,
+		uintptr(unsafe.Pointer(fdptr)),
+		uintptr(nfds),
+		uintptr(int(timeoutMillis)),
+		uintptr(unsafe.Pointer(nil)),
+		uintptr(unsafe.Pointer(nil)),
+		uintptr(unsafe.Pointer(nil)))
+	return int(n1), sys.UnwrapOSError(err)
+}
+
+// libc_poll_trampoline_addr is the address of the
+// `libc_poll_trampoline` symbol, defined in `poll_darwin.s`.
+//
+// We use this to invoke the syscall through syscall_syscall6 imported below.
+var libc_poll_trampoline_addr uintptr
+
+// Imports the select symbol from libc as `libc_poll`.
+//
+// Note: CGO mechanisms are used in darwin regardless of the CGO_ENABLED value
+// or the "cgo" build flag. See /RATIONALE.md for why.
+//go:cgo_import_dynamic libc_poll poll "/usr/lib/libSystem.B.dylib"