cmake/BuildArrow: Use system xsimd when available

cmake/BuildArrow: Use system xsimd when available

Arrow requires xsimd >= 9.0.1 according to arrow/cpp/thirdparty/versions.txt.
Previously, we unconditionally used the bundled xsimd version. This change
attempts to find a system xsimd package and only falls back to the bundled
version if the system package is not found or has an insufficient version.

This allows systems with libxsimd-dev >= 9.0.1 installed to use the system
package, reducing build time and dependencies.

Distribution availability:
- Ubuntu Noble (24.04): 12.1.1 (✓ sufficient)
- Ubuntu Jammy (22.04): 7.6.0 (✗ insufficient, will use bundled)
- Debian Trixie (13): 13.2.0 (✓ sufficient)

Signed-off-by: Kefu Chai <k.chai@proxmox.com>