Minimal executable, cleaned up from vendor code

- Removed extraneous and/or oversized(?) align from linker script
- Handle init_array properly
- Remove legacy init code paths (.ctors, .init)
- Don't do nonstandard interrupt mode handling by default

minimal-payload/main.c

@@ -0,0 +1,25 @@
+int test = 0x12345;
+int test2;
+
+#pragma GCC diagnostic ignored "-Wprio-ctor-dtor"
+__attribute__((constructor(0))) static void setup_qingke() {
+    asm volatile(
+        // Undocumented "Configure pipelining and instruction prediction"
+        "li t0, 0x1f\n"
+        "csrw 0xbc0, t0\n"
+    );
+}
+
+__attribute__((constructor)) static void constructor() {
+    test2 = 0x5678;
+}
+
+__attribute__((destructor)) static void destructor() {
+    test2 = 0x9abc;
+}
+
+int main(void) {
+    test++;
+    test2--;
+    return 123;
+}