wasm: use wasip1 API for parameter/env passing

Instead of hardcoding the command line parameters and the environment
variables in the binary, pass them at runtime to Node.js and use the
WASIp1 API to retrieve them in wasm_exec.js.

The only real benefit right now is that it becomes possible to change
`go.argv` and `go.env` before running a wasm binary.

This also changes the syscall package for GOOS=js: it now becomes more
like a libc (using wasi-libc), which means error values like
`syscall.EEXIST` will actually match the one returned by the relevant
libc function.

Wasm binary size for packages that import the os package will be
increased somewhat.

main.go

@@ -770,12 +770,11 @@ func Run(pkgName string, options *compileopts.Options, cmdArgs []string) error {
 // for the given emulator.
 func buildAndRun(pkgName string, config *compileopts.Config, stdout io.Writer, cmdArgs, environmentVars []string, timeout time.Duration, run func(cmd *exec.Cmd, result builder.BuildResult) error) (builder.BuildResult, error) {
 	// Determine whether we're on a system that supports environment variables
-	// and command line parameters (operating systems, WASI) or not (baremetal,
-	// WebAssembly in the browser). If we're on a system without an environment,
-	// we need to pass command line arguments and environment variables through
-	// global variables (built into the binary directly) instead of the
-	// conventional way.
-	needsEnvInVars := config.GOOS() == "js"
+	// and command line parameters (operating systems, WASI) or not (baremetal).
+	// If we're on a system without an environment, we need to pass command line
+	// arguments and environment variables through global variables (built into
+	// the binary directly) instead of the conventional way.
+	needsEnvInVars := false
 	for _, tag := range config.BuildTags() {
 		if tag == "baremetal" {
 			needsEnvInVars = true