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.0.zig

@@ -0,0 +1,15 @@
+pub fn main() void {
+    add(3, 4);
+}
+
+fn add(a: u32, b: u32) void {
+    assert(a + b == 7);
+}
+
+pub fn assert(ok: bool) void {
+    if (!ok) unreachable; // assertion failure
+}
+
+// run
+// target=x86_64-macos,x86_64-linux
+// link_libc=true