Emit INTRINSIC_ADD_CONDITIONAL_ANNOTATION for 3.16 conditional annotations

Summary:
CPython gh-154902 changed how a conditional annotation's index is registered
into the `__conditional_annotations__` set: instead of `SET_ADD`, 3.16 emits the
new `INTRINSIC_ADD_CONDITIONAL_ANNOTATION` binary intrinsic
(`CALL_INTRINSIC_2`). This diff mirrors that in cinderx's static bytecode
compiler.

Extract the emission into `CodeGenerator.emit_add_conditional_annotation()`
(default: `SET_ADD 1`, preserving 3.12/3.14/3.15 output) and override it in
`CodeGenerator316` to emit `CALL_INTRINSIC_2 INTRINSIC_ADD_CONDITIONAL_ANNOTATION`.
The intrinsic index resolves via `emit_call_intrinsic_2`, which reads it from the
running interpreter's opcode table, so it stays correct across versions.

Fixes the 3.16 cinderx compiler-test breakage from the CPython main sync
(SET_ADD vs CALL_INTRINSIC_2 disassembly mismatch).

Reviewed By: DinoV

Differential Revision: D115052327

fbshipit-source-id: 393d4d487fd7145c0c9af68632048236df671c4a

Author: itamaro

cinderx/PythonLib/cinderx/compiler/pycodegen.py

@@ -5992,9 +5992,14 @@ def emit_simple_ann_assign(self, node: ast.AnnAssign) -> None:
                 "__conditional_annotations__",
             )
             self.emit("LOAD_CONST", conditional_index)
-            self.emit("SET_ADD", 1)
+            self.emit_add_conditional_annotation()
             self.emit("POP_TOP")
 
+    def emit_add_conditional_annotation(self) -> None:
+        # Register the annotation's index into the `__conditional_annotations__`
+        # set that is on top of the stack (below the just-loaded index).
+        self.emit("SET_ADD", 1)
+
     def setup_annotations(
         self,
         loc: AST | SrcLocation,
@@ -6854,6 +6859,11 @@ class CodeGenerator316(CodeGenerator315):
     # result is discarded (used as an expression statement).
     _unused_listcomp_avoids_creation: bool = True
 
+    def emit_add_conditional_annotation(self) -> None:
+        # gh-154902: 3.16 registers a conditional annotation's index via the new
+        # INTRINSIC_ADD_CONDITIONAL_ANNOTATION binary intrinsic instead of SET_ADD.
+        self.emit_call_intrinsic_2("INTRINSIC_ADD_CONDITIONAL_ANNOTATION")
+
     def make_annotations_code_holder(self, code_gen: CodeGenerator) -> CodeHolder:
         # 3.16 extended the ".format" -> "format" rename to the
         # typevar-bound/default and type-alias-value scopes (CPython's