fix os2.process_exec on non-windows and add a smoke test

tests/core/normal.odin

@@ -33,6 +33,7 @@ download_assets :: proc() {
 @(require) import "net"
 @(require) import "odin"
 @(require) import "os"
+@(require) import "os/os2"
 @(require) import "path/filepath"
 @(require) import "reflect"
 @(require) import "runtime"

tests/core/os/os2/process.odin

@@ -0,0 +1,28 @@
+package tests_core_os_os2
+
+import    "base:runtime"
+
+import    "core:log"
+import os "core:os/os2"
+import    "core:testing"
+
+_ :: log
+
+@(test)
+test_process_exec :: proc(t: ^testing.T) {
+	state, stdout, stderr, err := os.process_exec({
+		command = {"echo", "hellope"},
+	}, context.allocator)
+	defer delete(stdout)
+	defer delete(stderr)
+
+	when (ODIN_OS not_in runtime.Odin_OS_Types{.Linux, .Darwin, .Windows}) {
+		testing.expect_value(t, err, os.General_Error.Unsupported)
+		_ = state
+	} else {
+		testing.expect_value(t, state.exited,  true)
+		testing.expect_value(t, state.success, true)
+		testing.expect_value(t, err, nil)
+		testing.expect_value(t, string(stdout), "hellope\n")
+	}
+}