Unify incremental test cases and disable many

The self-hosted aarch64 backend is not currently functional due to the
Liveness changes. A previous commit disabled aarch64 on the behavior
tests; this commit disables it and arm for the test cases. Moreover, all
incremental test cases have been unified into shared cross-platform
cases, which can be gradually enabled as the backends improve.

test/cases/assert_function.2.zig

@@ -0,0 +1,21 @@
+pub fn main() void {
+    add(3, 4);
+}
+
+fn add(a: u32, b: u32) void {
+    const c = a + b; // 7
+    const d = a + c; // 10
+    const e = d + b; // 14
+    const f = d + e; // 24
+    const g = e + f; // 38
+    const h = f + g; // 62
+    const i = g + h; // 100
+    assert(i == 100);
+}
+
+pub fn assert(ok: bool) void {
+    if (!ok) unreachable; // assertion failure
+}
+
+// run
+//