coverage: Migrate tests/run-coverage into tests/coverage

tests/coverage/simple_loop.rs

@@ -0,0 +1,35 @@
+#![allow(unused_assignments)]
+
+fn main() {
+    // Initialize test constants in a way that cannot be determined at compile time, to ensure
+    // rustc and LLVM cannot optimize out statements (or coverage counters) downstream from
+    // dependent conditions.
+    let is_true = std::env::args().len() == 1;
+
+    let mut countdown = 0;
+
+    if
+        is_true
+    {
+        countdown
+        =
+            10
+        ;
+    }
+
+    loop
+    {
+        if
+            countdown
+                ==
+            0
+        {
+            break
+            ;
+        }
+        countdown
+        -=
+        1
+        ;
+    }
+}