cmd/dist, sudo.bash: don't mention sudo.bash if cov or prof is not present

        Fixes #3422.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5967057

src/cmd/dist/build.c

@@ -1462,7 +1462,7 @@ void
 cmdbanner(int argc, char **argv)
 {
 	char *pathsep;
-	Buf b, b1, search;
+	Buf b, b1, search, path;
 
 	ARGBEGIN{
 	case 'v':
@@ -1478,6 +1478,7 @@ cmdbanner(int argc, char **argv)
 	binit(&b);
 	binit(&b1);
 	binit(&search);
+	binit(&path);
 
 	xprintf("\n");
 	xprintf("---\n");
@@ -1495,6 +1496,7 @@ cmdbanner(int argc, char **argv)
 		xprintf("*** You need to add %s to your PATH.\n", gobin);
 
 	if(streq(gohostos, "darwin")) {
+		if(isfile(bpathf(&path, "%s/cov", tooldir)))
 			xprintf("\n"
 				"On OS X the debuggers must be installed setgid procmod.\n"
 				"Read and run ./sudo.bash to install the debuggers.\n");
@@ -1509,6 +1511,7 @@ cmdbanner(int argc, char **argv)
 	bfree(&b);
 	bfree(&b1);
 	bfree(&search);
+	bfree(&path);
 }
 
 // Version prints the Go version.

src/sudo.bash

@@ -12,12 +12,17 @@ Darwin)
 	exit 0
 esac
 
+eval $(go env)
+if ! [ -x $GOTOOLDIR/cov -a -x $GOTOOLDIR/prof ]; then
+	echo "You don't need to run sudo.bash." >&2
+	exit 2
+fi
+
 if [[ ! -d /usr/local/bin ]]; then
 	echo 1>&2 'sudo.bash: problem with /usr/local/bin; cannot install tools.'
 	exit 2
 fi
 
-eval $(go env)
 cd $(dirname $0)
 for i in prof cov
 do