all: move bootstrapping IR to Go runtime

This has the benefit of not requiring a 'runtime' IR file, so that
complete relocatable files can be built without requiring input IR.
This makes the compiler a lot easier to use without the Makefile.

Code size is not affected.

src/runtime/runtime.go

@@ -6,6 +6,39 @@ import (
 
 const Compiler = "tgo"
 
+// The compiler will fill this with calls to the initialization function of each
+// package.
+func initAll()
+
+// These signatures are used to call the correct main function: with scheduling
+// or without scheduling.
+func main_main()
+func main_mainAsync(parent *coroutine) *coroutine
+
+// The compiler will change this to true if there are 'go' statements in the
+// compiled program and turn it into a const.
+var hasScheduler bool
+
+// Entry point for Go. Initialize all packages and call main.main().
+//go:export main
+func main() int {
+	// Run initializers of all packages.
+	initAll()
+
+	// This branch must be optimized away. Only one of the targets must remain,
+	// or there will be link errors.
+	if hasScheduler {
+		// Initialize main and run the scheduler.
+		coro := main_mainAsync(nil)
+		scheduler(coro)
+		return 0
+	} else {
+		// No scheduler is necessary. Call main directly.
+		main_main()
+		return 0
+	}
+}
+
 func Sleep(d Duration) {
 	// This function is treated specially by the compiler: when goroutines are
 	// used, it is transformed into a llvm.coro.suspend() call.

src/runtime/runtime.ll

@@ -1,27 +1,3 @@
 source_filename = "runtime/runtime.ll"
 
-declare void @runtime.initAll()
-declare void @main.main()
-declare i8* @main.main$async(i8*)
-declare void @runtime.scheduler(i8*)
-
-; Will be changed to true if there are 'go' statements in the compiled program.
-@has_scheduler = private unnamed_addr constant i1 false
-
-define i32 @main() {
-    call void @runtime.initAll()
-    %has_scheduler = load i1, i1* @has_scheduler
-    ; This branch will be optimized away. Only one of the targets will remain.
-    br i1 %has_scheduler, label %with_scheduler, label %without_scheduler
-
-with_scheduler:
-    ; Initialize main and run the scheduler.
-    %main = call i8* @main.main$async(i8* null)
-    call void @runtime.scheduler(i8* %main)
-    ret i32 0
-
-without_scheduler:
-    ; No scheduler is necessary. Call main directly.
-    call void @main.main()
-    ret i32 0
-}
+; dummy file

src/runtime/runtime_nrf.c

@@ -29,10 +29,6 @@ void RTC0_IRQHandler() {
 	rtc_wakeup = true;
 }
 
-void _start() {
-	main();
-}
-
 __attribute__((weak))
 void __aeabi_unwind_cpp_pr0() {
 	// dummy, not actually used

src/runtime/runtime_nrf.go

@@ -11,6 +11,11 @@ func _Cfunc_rtc_sleep(ticks uint32)
 
 const Microsecond = 1
 
+//go:export _start
+func _start() {
+	main()
+}
+
 func init() {
 	initUART()
 	initLFCLK()