pkg/60408: lang/zig tries to write to ~user/.cache/zig instead of $HOME/.cache/zig

>Number:         60408
>Category:       pkg
>Synopsis:       lang/zig tries to write to ~user/.cache/zig instead of $HOME/.cache/zig
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Jul 04 21:05:00 +0000 2026
>Originator:     Taylor R Campbell
>Release:        netbsd-11, pkgsrc-2026Q2
>Organization:
ZigBSD Home Improvements, Inc.
>Environment:
NetBSD manticore.local 11.0 NetBSD 11.0 (LIBKVER) #0: Tue Jan 19 00:00:00 UTC 2038 root@localhost:/sys/arch/amd64/compile/LIBKVER amd64

(really: NetBSD 11.0_RC5 kernel and userland)

BUILD_START_DIR=20260701.1613
>Description:
===> Installing for zig-0.16.0
=> Generating pre-install file lists
[ 35%] Built target zigcpp
[ 47%] Built target zig-wasm2c
[ 70%] Built target zig1
[100%] Built target zig2
Install the project...
-- Install configuration: "Release"
error: unable to open global cache directory '/pbulk/.cache/zig': ReadOnlyFileSystem
If this location is not writable then consider specifying an alternative with the ZIG_GLOBAL_CACHE_DIR environment variable or the --global-cache-dir option.
::
:: ERROR: 1
:: (execute_process)
::
:: argv: /tmp/pkgbuild/lang/zig/work/zig-0.16.0/cmake-pkgsrc-build/zig2 build --prefix /pkg/2026Q2 --zig-lib-dir /tmp/pkgbuild/lang/zig/work/zig-0.16.0/lib -Dversion-string=0.16.0 -Dtarget=native -Dcpu=baseline -Denable-llvm -Dconfig_h=/tmp/pkgbuild/lang/zig/work/zig-0.16.0/cmake-pkgsrc-build/config.h -Dno-langref -Doptimize=ReleaseFast -Dstrip


>How-To-Repeat:
cd lang/zig && bmake package
>Fix:
Yes, please!

If zig can't easily be patched, perhaps we should set ZIG_GLOBAL_CACHE_DIR.