XNNPACK Wasm benchmark

Benchmark built for wasm simd and relaxed simd after commit 2b5df08.

Function names with wasmsimd or relaxedsimd or wasmusdot or wasmsdot are candidates for V8 revectorization.
E.g.:
xnn_qs8_vadd_minmax_ukernel__wasmsimd_u32
xnn_f32_gemm_minmax_ukernel_1x8__wasmrelaxedsimd_fma_loadspla
xnn_qs8_qc8w_gemm_minmax_fp32_ukernel_1x16c4__wasmsdot_u2
xnn_qs8_qc8w_igemm_minmax_fp32_ukernel_1x16c4__wasmusdot_u2