Fixup using prebuilt JIT on ELN

See f45779a0aa for context.

After autoconf 2.73 landed in Fedora ELN,
the pre-built JIT stencils were rejected because of checksum mismatch.

This new patch adds an ability to circumvent that check.

It has been offered upstream in
https://github.com/python/cpython/issues/148646
https://github.com/python/cpython/pull/148647

While this has yet to be finalized upstream and might take a while, we need to fix the ELN build right away.

(When we build the stencils on rawhide for the next release,
the problem will shift from ELN with new autoconf to old Fedoras with old autoconf.)

Cherry-picked from python3.15 commit 4a1f3dae4f24af60227469c76acf9452f02c90dd

python3.14.spec

@@ -87,7 +87,7 @@ License: Python-2.0.1
 %bcond jit_build_stencils %[%{with jit} && 0%{?fedora} >= 41]
 %if %{with jit}
 # When built with JIT, it still needs to be enabled on runtime via PYTHON_JIT=1
-%global jit_flag --enable-experimental-jit=yes-off
+%global jit_flag --enable-experimental-jit=yes-off %{!?with_jit_build_stencils:--enable-prebuilt-jit-stencils}
 %endif
 
 # Main interpreter loop optimization
@@ -471,6 +471,10 @@ Patch481: 00481-cve-2026-5713.patch
 # Fix a possible UAF in {LZMA,BZ2,_Zlib}Decompressor
 Patch482: 00482-cve-2026-6100.patch
 
+# 00486 # 5ae0b81b3135319f8d75a886fb7a11fa40ac11f4
+# gh-148646: Add --enable-prebuilt-jit-stencils configure flag
+Patch486: 00486-gh-148646-add---enable-prebuilt-jit-stencils-configure-flag.patch
+
 # (New patches go here ^^^)
 #
 # When adding new patches to "python" and "python3" in Fedora, EL, etc.,