test: Don't run "go build" each time a helper is invoked

Our tests invoke a variety of helpers, some of them are written in Go.
Today, we call "go build" (directly or indirectly via "go run"), which is
a bit wasteful and slows down the tests.

This patch makes the tests only build our Go helpers once every 10s at
most.

The solution is a bit hacky but in the context of these tests, it's
practical.

test/t-04-aliases/run.sh

@@ -74,6 +74,8 @@ fi
 
 # Test chasquid-util's ability to do alias resolution talking to chasquid.
 # We use chamuyero for convenience, so we can match the output exactly.
+# We run it once to ensure it gets built.
+chasquid-util --help > /dev/null
 for i in *.cmy; do
 	if ! chamuyero "$i" > "$i.log" 2>&1 ; then
 		echo "$i failed, log follows"