support `garble run`

It's the third time I've wanted it to quickly test out standalone
reproducers when people submit bugs.

Fixes #661.

README.md

@@ -7,6 +7,7 @@ Obfuscate Go code by wrapping the Go toolchain. Requires Go 1.20 or later.
 	garble build [build flags] [packages]
 
 The tool also supports `garble test` to run tests with obfuscated code,
+`garble run` to obfuscate and execute simple programs,
 and `garble reverse` to de-obfuscate text such as stack traces.
 See `garble -h` for up to date usage information.
 

main.go

@@ -121,6 +121,7 @@ The following commands are supported:
 
 	build          replace "go build"
 	test           replace "go test"
+	run            replace "go run"
 	reverse        de-obfuscate output such as stack traces
 	version        print the version and build settings of the garble binary
 
@@ -396,7 +397,7 @@ func mainErr(args []string) error {
 		return nil
 	case "reverse":
 		return commandReverse(args)
-	case "build", "test":
+	case "build", "test", "run":
 		cmd, err := toolexecCmd(command, args)
 		defer os.RemoveAll(os.Getenv("GARBLE_SHARED"))
 		if err != nil {

testdata/script/run.txtar

@@ -0,0 +1,29 @@
+garble run garble_main.go
+! stdout '^garble_main\.go 9$'
+stdout '\.go \d'
+
+[short] stop # no need to verify this with -short
+
+# also with a package
+garble run .
+! stdout '^garble_main\.go 9$'
+stdout '\.go \d'
+
+go run garble_main.go
+stdout 'garble_main\.go 9$'
+-- go.mod --
+module test/main
+
+go 1.20
+-- garble_main.go --
+package main
+
+import (
+	"fmt"
+	"runtime"
+)
+
+func main() {
+	_, file, line, _ := runtime.Caller(0)
+	fmt.Println(file, line)
+}