main: add -debug flag that controls debuginfo stripping

Debug information is useful in many case, but in the case of WebAssembly
it increases the binary size by a large amount. It also inhibits
compression of relocations. Therefore I've made debug information
optional and disabled by default.

(Debug information is still generated, but stripped from the binary at
the link step).

compileopts/options.go

@@ -9,6 +9,7 @@ import (
 var (
 	validGCOptions            = []string{"none", "leaking", "extalloc", "conservative"}
 	validSchedulerOptions     = []string{"none", "tasks", "coroutines"}
+	validDebugOptions         = []string{"auto", "true", "false"}
 	validSerialOptions        = []string{"none", "uart", "usb"}
 	validPrintSizeOptions     = []string{"none", "short", "full"}
 	validPanicStrategyOptions = []string{"print", "trap"}
@@ -28,7 +29,8 @@ type Options struct {
 	DumpSSA         bool
 	VerifyIR        bool
 	PrintCommands   func(cmd string, args ...string)
-	Debug           bool
+	EmitDWARF       bool
+	Debug           string
 	PrintSizes      string
 	PrintAllocs     *regexp.Regexp // regexp string
 	PrintStacks     bool
@@ -70,6 +72,12 @@ func (o *Options) Verify() error {
 		}
 	}
 
+	if !isInArray(validDebugOptions, o.Debug) {
+		return fmt.Errorf(`invalid debug option '%s': valid values are %s`,
+			o.Debug,
+			strings.Join(validDebugOptions, ", "))
+	}
+
 	if o.PrintSizes != "" {
 		valid := isInArray(validPrintSizeOptions, o.PrintSizes)
 		if !valid {