Gentoo LLVM_TARGETS not Working?

Recently, I would like to test switching from gcc to clang on my Gentoo VM.
~~warning: you will be crazy to have too many packages can't be build with clang~~

1. problem

First I want to make LLVM not targeting too many platform, but changing LLVM_TARGETS don't work

[ebuild  N     ] sys-devel/llvm-15.0.3:15::gentoo  USE="binutils-plugin libffi
ncurses -debug -doc -exegesis -libedit -test -verify-sig -xar -xml -z3 -zstd"
LLVM_TARGETS="(AArch64) (AMDGPU) (ARM) (AVR) (BPF) (Hexagon) (Lanai) (MSP430)
(Mips) (NVPTX) (PowerPC) (RISCV) (Sparc) (SystemZ) (VE) (WebAssembly) (X86)
(XCore) (-ARC) (-CSKY) (-DirectX) (-LoongArch) (-M68k) (-SPIRV)" 241 KiB

2. and I found [solved] LLVM_TARGETS not respected?(Mar 2022) on gentoo forum

It seems that global LLVM_TARGETS setting is not respected,
and flags such as llvm_targets_AArch64, llvm_targets_ARM, are no longer there.
They're now forced by default as a precaution.

3. solution

3.1. add something like `/ -llvm_targets_AArch64` into `/etc/portage/profile/package.use.force`

I excluded all targets exept for X86, but still 3 left: AMDGPU, BPF, NVPTX

3.2. so I also add `sys-devel/llvm -llvm_targets_AMDGPU -llvm_targets_BPF -llvm_targets_NVPTX` in `/etc/portage/package.use/`

3.3. and don't forget to add that three excluder to clang or other compiler that uses llvm

4. finally I got this:

[ebuild  N     ] sys-devel/llvm-15.0.3:15::gentoo  USE="binutils-plugin libffi
ncurses -debug -doc -exegesis -libedit -test -verify-sig -xar -xml -z3 -zstd"
LLVM_TARGETS="(X86) -AArch64 -AMDGPU (-ARC) -ARM -AVR -BPF (-CSKY) (-DirectX)
-Hexagon -Lanai (-LoongArch) (-M68k) -MSP430 -Mips -NVPTX -PowerPC -RISCV
(-SPIRV) -Sparc -SystemZ -VE -WebAssembly -XCore" 241 KiB