zig: Downgrade to 0.13 with local LLVM (#4844)

**Summary**

Bring back Zig from 0.14 snapshot to stable 0.13 release using in-tree
LLVM build.

**Test Plan**

- Built `ghostty`
- Zig x86 test suite all passed.

**Checklist**

- [x] Package was built and tested against unstable
- [ ] This change could gainfully be listed in the weekly sync notes
once merged <!-- Write an appropriate message in the Summary section,
then add the "Topic: Sync Notes" label -->

packages/z/zig/abi_used_libs

@@ -1,8 +1,5 @@
 ld-linux-x86-64.so.2
-libLLVM.so.19.1
 libc.so.6
-libclang-cpp.so.19.1
-liblldCOFF.so.19.1
-liblldELF.so.19.1
-liblldWasm.so.19.1
-libstdc++.so.6
+libm.so.6
+libz.so.1
+libzstd.so.1