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.18.zig

@@ -0,0 +1,20 @@
+const builtin = @import("builtin");
+
+extern "c" fn write(c_int, usize, usize) usize;
+
+pub fn main() void {
+    for ("hello") |_| print();
+}
+
+fn print() void {
+    _ = write(1, @ptrToInt("hello\n"), 6);
+}
+
+// run
+//
+// hello
+// hello
+// hello
+// hello
+// hello
+//