Build GMP as a fat library to support older CPUs

--enable-fat selects the optimized code at run time, so the static
library also works on x86_64 CPUs without AVX, BMI2 or ADX. It is
ignored on architectures that do not support it, such as aarch64.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

alpine3.24/Dockerfile

@@ -461,7 +461,7 @@ RUN --mount=type=bind,from=sources,source=gmp-6.3.0.tar.xz,target=/tmp/gmp.tar.x
     mkdir src \
     && tar --extract --xz --file=/tmp/gmp.tar.xz --directory=src --strip-components=1 \
     && cd src \
-    && CFLAGS="-fPIC -std=gnu17" ./configure --prefix=/usr/local --disable-shared --enable-static \
+    && CFLAGS="-fPIC -std=gnu17" ./configure --prefix=/usr/local --disable-shared --enable-static --enable-fat \
     && make --jobs="$(nproc)" \
     && make install \
     && cd .. \