[3.15] gh-151126: Fix missing PyErr_NoMemory() in remove_unused_consts (GH-151127) (#151134)

gh-151126: Fix missing `PyErr_NoMemory()` in `remove_unused_consts` (GH-151127)
(cherry picked from commit 3186547)

Co-authored-by: sobolevn <mail@sobolevn.me>

Author: miss-islington

Misc/NEWS.d/next/Core_and_Builtins/2026-06-09-10-28-30.gh-issue-151126.DKa6Sl.rst

@@ -0,0 +1,3 @@
+Fix a crash, when there's no memory left on a device,
+which happened in code compilation.
+Now it raises a proper :exc:`MemoryError`.

Python/flowgraph.c

@@ -3273,6 +3273,7 @@ remove_unused_consts(basicblock *entryblock, PyObject *consts)
 
     index_map = PyMem_Malloc(nconsts * sizeof(Py_ssize_t));
     if (index_map == NULL) {
+        PyErr_NoMemory();
         goto end;
     }
     for (Py_ssize_t i = 1; i < nconsts; i++) {
@@ -3325,6 +3326,7 @@ remove_unused_consts(basicblock *entryblock, PyObject *consts)
     /* adjust const indices in the bytecode */
     reverse_index_map = PyMem_Malloc(nconsts * sizeof(Py_ssize_t));
     if (reverse_index_map == NULL) {
+        PyErr_NoMemory();
         goto end;
     }
     for (Py_ssize_t i = 0; i < nconsts; i++) {