SECURITY UPDATE: out-of-bounds memory access from an unbounded stack
allocation in the SPIR-V front end (ELSCVE-171724)
debian/patches/backport-STACK_ARRAY.patch: add the upstream
src/util/stack_array.h helper, which the fix requires.
debian/patches/CVE-2026-40393.patch: replace NIR_VLA, a bare alloca,
with STACK_ARRAY at the two sites whose element count comes from the
shader, in src/compiler/spirv/spirv_to_nir.c and
src/compiler/nir/nir_inline_functions.c.