Support Linux on MIPS and ARMv5TE

Ensure to set num threads to 1 for thread pools when `num_cpus::get()` returns 0.

src/common/thread_pool.rs

@@ -53,7 +53,10 @@ impl ThreadPoolRegistry {
                 // and insert a new pool.
                 let mut pools = REGISTRY.pools.write();
                 pools.entry(name).or_insert_with(|| {
-                    let num_threads = num_cpus::get();
+                    // Some platforms may return 0. In that case, use 1.
+                    // https://github.com/moka-rs/moka/pull/39#issuecomment-916888859
+                    // https://github.com/rust-lang/futures-rs/pull/1835
+                    let num_threads = num_cpus::get().max(1);
                     let pool =
                         ScheduledThreadPool::with_name(name.thread_name_template(), num_threads);
                     let t_pool = ThreadPool {