add rp6502 target

libsrc/rp6502/read_xstack.c

@@ -0,0 +1,22 @@
+/*
+ * Copyright (c) 2023 Rumbledethumps
+ *
+ * SPDX-License-Identifier: Zlib
+ * SPDX-License-Identifier: BSD-3-Clause
+ * SPDX-License-Identifier: Unlicense
+ */
+
+#include <rp6502.h>
+
+int __fastcall__ read_xstack(void *buf, unsigned count, int fildes)
+{
+    int i, ax;
+    ria_push_int(count);
+    ria_set_ax(fildes);
+    ax = ria_call_int_errno(RIA_OP_READ_XSTACK);
+    for (i = 0; i < ax; i++)
+    {
+        ((char *)buf)[i] = ria_pop_char();
+    }
+    return ax;
+}