python-plugin: RAII (PyOwned/PyBorrowed) + autodecode enum; crate: ny-llvmc --emit exe with NyRT link; tools: build_llvm.sh crate-exe path + crate_exe_smoke; CURRENT_TASK update

plugins/nyash-python-plugin/src/gil.rs

@@ -0,0 +1,19 @@
+use crate::ffi::{CPython, PyGILState_STATE};
+
+pub struct GILGuard<'a> {
+    cpy: &'a CPython,
+    state: PyGILState_STATE,
+}
+
+impl<'a> GILGuard<'a> {
+    pub fn acquire(cpy: &'a CPython) -> Self {
+        let state = unsafe { (cpy.PyGILState_Ensure)() };
+        GILGuard { cpy, state }
+    }
+}
+
+impl<'a> Drop for GILGuard<'a> {
+    fn drop(&mut self) {
+        unsafe { (self.cpy.PyGILState_Release)(self.state) };
+    }
+}