tools/build: use separate tmp dirs for parallel builds

[greatgitsby]

Summary

• Use tmp-kernel and tmp-system instead of shared tmp dir so kernel and system builds can run concurrently without conflicts

Test plan

• Run kernel and system builds in parallel
• Confirm build outputs are still in build/

Generated with Claude Code

[github-actions]

vamOS System Profile

Changes vs master

Metric	Change
Used space	3442.3MB → 3442.3MB (+0MB)
Sparse image	3380.4MB → 3382.3MB (+1.9MB)
Package count	517 → 517

Added packages: kitty-terminfo-0.46.2_1

Removed packages: kitty-terminfo-0.45.0_1

Directory size changes (>1MB)

Directory	Change

---

Metric	Value
Used space	3442.3MB / 5959.5MB
Files	55613
Directories	4418
Symlinks	3448
Packages	517

Top 10 Directories

Directory	Size

Category Breakdown

Category	Size	%
xbps packages	2477.7MB	71.9%
Python venv	639.3MB	18.5%
Firmware	1.2MB	0%
Other	324.0MB	9.4%

Top 10 Packages by Size

Package	Size
mit-krb5-libs-1.21.3_1	270.4MB
gawk-5.3.2_1	210.3MB
llvm-21_3	148.6MB
libldns-1.9.0_1	124.3MB
pcre2-devel-10.47_1	74MB
libclang21-21.1.7_1	70.2MB
glib-2.86.1_2	67.1MB
gcc-14.2.1+20250405_4	65.4MB
libcap-progs-2.77_1	56MB
cmake-4.2.2_1	53.2MB

Top 30 Files by Size

File	Size
/usr/lib/llvm/21/lib/libLLVM.so.21.1	124.3MB
/usr/lib/llvm/21/lib/libMLIR.so.21.1	89.7MB
/usr/lib/llvm/21/bin/mlir-transform-opt	82.9MB
/usr/lib/llvm/21/lib/libclang-cpp.so.21.1	56MB
/usr/lib/llvm/21/bin/mlir-translate	53.2MB
/usr/lib/llvm/21/bin/llvm-exegesis	52MB
/usr/lib/llvm/21/bin/llvm-bolt-binary-analysis	50.6MB
/usr/bin/uv	46.3MB
/usr/local/venv/lib/python3.12/site-packages/ffmpeg/install/lib/libavcodec.a	40.3MB
/usr/lib/gcc/aarch64-linux-gnu/14.2/gnat1	40.1MB
/usr/bin/gdb	38.1MB
/usr/lib/gcc/aarch64-linux-gnu/14.2/cc1plus	37.3MB
/usr/lib/libgallium-25.3.3.so	35.4MB
/usr/lib/libllvm-qcom.so	35.2MB
/usr/lib/gcc/aarch64-linux-gnu/14.2/cc1	35.2MB
/usr/lib/gcc/aarch64-linux-gnu/14.2/lto1	33.9MB
/usr/bin/lto-dump	33.9MB
/usr/lib/libRusticlOpenCL.so.1.0.0	32.5MB
/usr/local/venv/bin/ruff	31.8MB
/usr/share/icu/78.2/icudt78l.dat	31.5MB
/usr/lib/llvm/21/lib/libclang.so.21.1.7	30.2MB
/usr/lib/llvm/21/bin/c-index-test	28.6MB
/usr/local/venv/lib/python3.12/site-packages/gcc_arm_none_eabi/toolchain/libexec/gcc/arm-none-eabi/13.2.1/cc1	28.2MB
/usr/lib/libz3.so	27.9MB
/usr/bin/run	26.6MB
/usr/local/venv/lib/python3.12/site-packages/numpy.libs/libscipy_openblas64_-71e1b124.so	23.6MB
/usr/comma/updater	23.5MB
/usr/comma/setup	23.5MB
/usr/comma/reset	23.5MB
/usr/local/uv/python/cpython-3.12.13-linux-aarch64-gnu/bin/python3.12	21.6MB

[adeebshihadeh]

I suggest using mktemp -d so that you can even do parallel kernel and system builds.