Add llvm code model option in target definition

compileopts/target.go

@@ -276,6 +276,7 @@ func defaultTarget(goos, goarch, triple string) (*TargetSpec, error) {
 		GDB:         "gdb",
 		PortReset:   "false",
 		FlashMethod: "native",
+		CodeModel:   "default",
 	}
 	if goos == "darwin" {
 		spec.LDFlags = append(spec.LDFlags, "-Wl,-dead_strip")

targets/maixbit.ld

@@ -1,7 +1,7 @@
 
 MEMORY
 {
-    RAM (xrw) : ORIGIN = 0xffffffff80000000, LENGTH = 6M
+    RAM (xrw) : ORIGIN = 0x80000000, LENGTH = (6 * 1024 * 1024)
 }
 
 REGION_ALIAS("FLASH_TEXT", RAM);