main: remove -target flag for LLVM targets

It is better to use environment variables (GOOS and GOARCH) for
consistency instead of providing two slightly incompatible ways. This
-target flag should only be used to specify a .json file (either
directly or in the TinyGo targets directory). Previously it was possible
to specify the LLVM target as well but that was never really fully
supported.

So:

  - To specify a different OS/arch like you would in regular Go, use
    GOOS and GOARCH.
  - To specify a microcontroller chip or board, use the -target flag.

Also remove the old `os.Setenv` which might have had a purpose long ago
but doesn't have a purpose now.

compileopts/target.go

@@ -189,41 +189,16 @@ func LoadTarget(options *Options) (*TargetSpec, error) {
 	// Arduino).
 	spec := &TargetSpec{}
 	err := spec.loadFromGivenStr(options.Target)
-	if err == nil {
-		// Successfully loaded this target from a built-in .json file. Make sure
-		// it includes all parents as specified in the "inherits" key.
-		err = spec.resolveInherits()
-		if err != nil {
-			return nil, err
-		}
-		return spec, nil
-	} else if !os.IsNotExist(err) {
-		// Expected a 'file not found' error, got something else. Report it as
-		// an error.
+	if err != nil {
 		return nil, err
-	} else {
-		// Load target from given triple, ignore GOOS/GOARCH environment
-		// variables.
-		tripleSplit := strings.Split(options.Target, "-")
-		if len(tripleSplit) < 3 {
-			return nil, errors.New("expected a full LLVM target or a custom target in -target flag")
-		}
-		goos := tripleSplit[2]
-		if strings.HasPrefix(goos, "darwin") {
-			goos = "darwin"
-		}
-		goarch := map[string]string{ // map from LLVM arch to Go arch
-			"i386":    "386",
-			"i686":    "386",
-			"x86_64":  "amd64",
-			"aarch64": "arm64",
-			"armv7":   "arm",
-		}[tripleSplit[0]]
-		if goarch == "" {
-			goarch = tripleSplit[0]
-		}
-		return defaultTarget(goos, goarch, strings.Join(tripleSplit, "-"))
 	}
+	// Successfully loaded this target from a built-in .json file. Make sure
+	// it includes all parents as specified in the "inherits" key.
+	err = spec.resolveInherits()
+	if err != nil {
+		return nil, err
+	}
+	return spec, nil
 }
 
 // WindowsBuildNotSupportedErr is being thrown, when goos is windows and no target has been specified.

compileopts/target_test.go

@@ -1,6 +1,7 @@
 package compileopts
 
 import (
+	"os"
 	"reflect"
 	"testing"
 )
@@ -16,7 +17,7 @@ func TestLoadTarget(t *testing.T) {
 		t.Error("LoadTarget should have failed with non existing target")
 	}
 
-	if err.Error() != "expected a full LLVM target or a custom target in -target flag" {
+	if !os.IsNotExist(err) {
 		t.Error("LoadTarget failed for wrong reason:", err)
 	}
 }

main.go

@@ -1081,7 +1081,7 @@ func main() {
 	dumpSSA := flag.Bool("dumpssa", false, "dump internal Go SSA")
 	verifyIR := flag.Bool("verifyir", false, "run extra verification steps on LLVM IR")
 	tags := flag.String("tags", "", "a space-separated list of extra build tags")
-	target := flag.String("target", "", "LLVM target | .json file with TargetSpec")
+	target := flag.String("target", "", "chip/board name or JSON target specification file")
 	printSize := flag.String("size", "", "print sizes (none, short, full)")
 	printStacks := flag.Bool("print-stacks", false, "print stack sizes of goroutines")
 	printAllocsString := flag.String("print-allocs", "", "regular expression of functions for which heap allocations should be printed")
@@ -1173,8 +1173,6 @@ func main() {
 		options.PrintCommands = printCommand
 	}
 
-	os.Setenv("CC", "clang -target="+*target)
-
 	err = options.Verify()
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err.Error())