compiler, runtime: enable go:wasmexport for wasip2 (#4499)

* compiler: prefer go:wasmexport over go:export

* runtime, targets/wasip2: enable -buildmode=c-shared for wasip2

* runtime: rename import from wasi_run to wasiclirun (PR feedback)

src/runtime/runtime_wasip2.go

@@ -0,0 +1,57 @@
+//go:build wasip2
+
+package runtime
+
+import (
+	"unsafe"
+
+	"internal/wasi/cli/v0.2.0/environment"
+	wasiclirun "internal/wasi/cli/v0.2.0/run"
+	monotonicclock "internal/wasi/clocks/v0.2.0/monotonic-clock"
+
+	"internal/cm"
+)
+
+type timeUnit int64
+
+func init() {
+	wasiclirun.Exports.Run = func() cm.BoolResult {
+		callMain()
+		return false
+	}
+}
+
+var args []string
+
+//go:linkname os_runtime_args os.runtime_args
+func os_runtime_args() []string {
+	if args == nil {
+		args = environment.GetArguments().Slice()
+	}
+	return args
+}
+
+//export cabi_realloc
+func cabi_realloc(ptr, oldsize, align, newsize unsafe.Pointer) unsafe.Pointer {
+	return realloc(ptr, uintptr(newsize))
+}
+
+func ticksToNanoseconds(ticks timeUnit) int64 {
+	return int64(ticks)
+}
+
+func nanosecondsToTicks(ns int64) timeUnit {
+	return timeUnit(ns)
+}
+
+func sleepTicks(d timeUnit) {
+	p := monotonicclock.SubscribeDuration(monotonicclock.Duration(d))
+	p.Block()
+}
+
+func ticks() timeUnit {
+	return timeUnit(monotonicclock.Now())
+}
+
+func beforeExit() {
+}