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.

ir.go

@@ -35,7 +35,8 @@ type Program struct {
 type Function struct {
 	fn           *ssa.Function
 	llvmFn       llvm.Value
-	linkName     string      // go:linkname pragma
+	linkName     string      // go:linkname or go:export pragma
+	exported     bool        // go:export
 	nobounds     bool        // go:nobounds pragma
 	blocking     bool        // calculated by AnalyseBlockingRecursive
 	flag         bool        // used by dead code elimination
@@ -178,11 +179,22 @@ func (f *Function) parsePragmas() {
 				if hasUnsafeImport(f.fn.Pkg.Pkg) {
 					f.nobounds = true
 				}
+			case "//go:export":
+				if len(parts) != 2 {
+					continue
+				}
+				f.linkName = parts[1]
+				f.exported = true
 			}
 		}
 	}
 }
 
+// Return true iff this function is externally visible.
+func (f *Function) IsExported() bool {
+	return f.exported
+}
+
 // Return the link name for this function.
 func (f *Function) LinkName() string {
 	if f.linkName != "" {