audioutils/lame: Add CMake vector sources.

[casaroli]

Summary

Fix the CMake build of the bundled LAME encoder for x86 simulator hosts.

LAME's generated configuration enables SSE2 and AVX2 runtime-dispatch paths when the host compiler supports their per-function target attributes. The CMake libmp3lame target omitted the corresponding vector translation units, which left sim:alsa with unresolved symbols at link time. This change adds the complete vector source group only for CONFIG_HOST_X86 and CONFIG_HOST_X86_64; non-x86 simulator hosts retain LAME's scalar implementation.

Companion NuttX PR: apache/nuttx#19541. It supplies the bundled codec header include paths required to compile sim_offload.c.

Impact

• New feature: No.
• User adaptation: No.
• Build impact: Yes. Fixes linking of CMake sim:alsa builds on x86 hosts when LAME enables its vector dispatch.
• Hardware impact: No. This is host-simulator build integration; x86 vector routines continue to be selected only by LAME's runtime CPU dispatch.
• Documentation impact: No.
• Security impact: No.
• Compatibility impact: No. Non-x86 hosts continue to compile and use the scalar LAME path.
• Dependency: must be merged with the companion NuttX codec-header PR for a complete sim:alsa CMake fix.

Testing

Verified locally with the companion NuttX branch.

• Build host: Fedora Linux 44, x86_64, GCC 16.1.1.
• Target: sim:alsa, CMake/Ninja, CONFIG_SIM_M32=y.

Before this change, after resolving the missing codec headers, the final link failed with unresolved LAME vector symbols:

undefined reference to `quantize_lines_xrpow_avx2'
undefined reference to `count_bit_esc_sse2'

After this change:

cmake -B build -DBOARD_CONFIG=sim:alsa -DNXTMPDIR=OFF -GNinja
cmake --build build -j4

completed successfully and produced nuttx.tgz.

Additional verification:

cmake-format --check audioutils/lame/CMakeLists.txt
git diff --check

Both completed successfully.

No hardware runtime test applies to this host simulator build.

PR verification self-check

• This PR introduces one focused functional change.
• All required PR description fields are completed.
• The commit has a descriptive topic/body, Signed-off-by, and Assisted-by trailer.
• The modified CMake file passes cmake-format and git diff --check.
• This PR is ready for review.

[cederom]

Thank you @casaroli :-)