Add setenv to standard library

src/rt/rust_builtin.cpp

@@ -650,6 +650,20 @@ rust_ptr_eq(rust_task *task, type_desc *t, rust_box *a, rust_box *b) {
     return a == b;
 }
 
+#if defined(__WIN32__)
+extern "C" CDECL int32_t
+rust_SetEnvironmentVariable(rust_task *task,
+                            const char *name, const char *val) {
+     return SetEnvironmentVariable(name, val);
+}
+
+extern "C" CDECL uint32_t
+rust_GetEnvironmentVariable(rust_task *task,
+                            const char *name, char *buf, uint32_t size) {
+    return GetEnvironmentVariable(name, buf, size);
+}
+#endif
+
 #if defined(__WIN32__)
 extern "C" CDECL void
 get_time(rust_task *task, uint32_t *sec, uint32_t *usec) {