all: check GOROOT_BOOTSTRAP executable before bootsrappping

Otherwise we’d still be writing that we're building cmd/dist
even if GOROOT_BOOTSTRAP we’re wrongly set.

Change-Id: I940e18c3cebae5664f85babc9919e9eb215d5093
Reviewed-on: https://go-review.googlesource.com/c/go/+/253877
Run-TryBot: Cuong Manh Le <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>

Author: cuonglm

src/make.bash

@@ -162,16 +162,16 @@ IFS=$'\n'; for go_exe in $(type -ap go); do
 		fi
 	fi
 done; unset IFS
-GOROOT_BOOTSTRAP_VERSION=$($GOROOT_BOOTSTRAP/bin/go version | sed 's/go version //')
-echo "Building Go cmd/dist using $GOROOT_BOOTSTRAP. ($GOROOT_BOOTSTRAP_VERSION)"
-if $verbose; then
-	echo cmd/dist
-fi
 if [ ! -x "$GOROOT_BOOTSTRAP/bin/go" ]; then
 	echo "ERROR: Cannot find $GOROOT_BOOTSTRAP/bin/go." >&2
 	echo "Set \$GOROOT_BOOTSTRAP to a working Go tree >= Go 1.4." >&2
 	exit 1
 fi
+GOROOT_BOOTSTRAP_VERSION=$($GOROOT_BOOTSTRAP/bin/go version | sed 's/go version //')
+echo "Building Go cmd/dist using $GOROOT_BOOTSTRAP. ($GOROOT_BOOTSTRAP_VERSION)"
+if $verbose; then
+	echo cmd/dist
+fi
 if [ "$GOROOT_BOOTSTRAP" = "$GOROOT" ]; then
 	echo "ERROR: \$GOROOT_BOOTSTRAP must not be set to \$GOROOT" >&2
 	echo "Set \$GOROOT_BOOTSTRAP to a working Go tree >= Go 1.4." >&2