- C:\im was outside the project so bin/spc reset could not clean it
- with the command line limit fixed a short base path is no longer
needed; keep SPC_IMAGEMAGICK_BUILD_DIR as an override
ax_gcc_archflag has no Zen cpuid pattern and falls back to
-mtune=amdfam10, which under LLVM+LTO emits SSE4a extrq and SIGILLs on
Intel hosts. Disable the implicit --with-gcc-arch so host CPU features
do not bleed into the built binaries.
