Get pokefirered_modern to build

src/main.c

@@ -90,7 +90,27 @@ void EnableVCountIntrAtLine150(void);
 
 void AgbMain()
 {
+#if MODERN
+    // Modern compilers are liberal with the stack on entry to this function,
+    // so RegisterRamReset may crash if it resets IWRAM.
+    RegisterRamReset(RESET_ALL & ~RESET_IWRAM);
+    asm("mov\tr1, #0xC0\n"
+        "\tlsl\tr1, r1, #0x12\n"
+        "\tmov r2, #0xFC\n"
+        "\tlsl r2, r2, #0x7\n"
+        "\tadd\tr2, r1, r2\n"
+        "\tmov\tr0, #0\n"
+        "\tmov\tr3, r0\n"
+        "\tmov\tr4, r0\n"
+        "\tmov\tr5, r0\n"
+        ".LCU0:\n"
+        "\tstmia r1!, {r0, r3, r4, r5}\n"
+        "\tcmp\tr1, r2\n"
+        "\tbcc\t.LCU0\n"
+    );
+#else
     RegisterRamReset(RESET_ALL);
+#endif //MODERN
     *(vu16 *)BG_PLTT = RGB_WHITE;
     InitGpuRegManager();
     REG_WAITCNT = WAITCNT_PREFETCH_ENABLE | WAITCNT_WS0_S_1 | WAITCNT_WS0_N_3;