maixbit (uart): serial is working with echo example

targets/riscv.json

@@ -16,9 +16,5 @@
 	"ldflags": [
 		"--gc-sections"
 	],
-	"extra-files": [
-		"src/device/riscv/start.S",
-		"src/runtime/scheduler_tinygoriscv.S"
-	],
 	"gdb": "riscv64-unknown-elf-gdb"
 }

targets/riscv32.json

@@ -1,6 +1,7 @@
 {
 	"inherits": ["riscv"],
 	"llvm-target": "riscv32--none",
+	"build-tags": ["tinygo.riscv32"],
 	"cflags": [
 		"--target=riscv32--none",
 		"-march=rv32imac",
@@ -8,5 +9,9 @@
 	],
 	"ldflags": [
 		"-melf32lriscv"
+	],
+	"extra-files": [
+		"src/runtime/scheduler_tinygoriscv.S",
+		"src/device/riscv/start.S"
 	]
 }

targets/riscv64.json

@@ -9,5 +9,9 @@
 	],
 	"ldflags": [
 		"-melf64lriscv"
+	],
+	"extra-files": [
+		"src/runtime/scheduler_tinygoriscv64.S",
+		"src/device/riscv/start64.S"
 	]
 }