Adds two thin one-liner-ish helpers that invoke `cmake` with the flag
set documented in docs/build.md "CPU build flags for AVX-512", so that
users on AMD Zen4 / Intel Sapphire Rapids+ hardware get the IQK
HAVE_FANCY_SIMD path activated without having to remember the five
relevant `GGML_AVX512_*=ON` options.
scripts/build-zen.sh - Linux / macOS bash wrapper
scripts/build-zen.bat - Windows MSVC wrapper (run from a
"x64 Native Tools Command Prompt")
Both default to a "build" output directory, both pass through to the
same cmake invocation, and both work alongside the existing build
options (no behavioural change to vanilla CMake builds).
.gitignore: added `!scripts/build-*.sh` / `!scripts/build-*.bat`
exceptions, in line with the existing `!build-info.sh` / `!build.zig`
exceptions, so the scripts directory build helpers don't get caught
by the broad `build*` artifact pattern.
This is a follow-up to #1729 — the docs section explains why these
flags matter, this PR makes them one command away.
a67287124d