golang: Provide ${go:exe}

${go:exe} is standalone executable that runs go in activated gowork environment.
It is handy to use in recipes where one cannot source ${gowork:env} -
in particular parts with recipe=zc.recipe.egg

Wendelin.core 2 will use `GO=${go:exe}` in its build environment.

component/golang/buildout.cfg

@@ -6,7 +6,7 @@ extends =
   ../git/buildout.cfg
   ../pkgconfig/buildout.cfg
 
-parts = gowork
+parts = gowork go
 
 # ---- Go builds itself ----
 
@@ -84,6 +84,18 @@ environment-extra =
 #
 #   [gowork]
 #   buildflags = -race
+#
+# ${go:exe} is standalone executable that runs go in activated gowork environment.
+[go]
+recipe  = slapos.recipe.template:jinja2
+exe     = ${buildout:bin-directory}/go
+rendered= ${:exe}
+mode    = 755
+template= inline:
+  #!/bin/sh -e
+  . ${gowork:env.sh}
+  exec go "$@"
+
 [gowork]
 directory = ${buildout:directory}/go.work
 src	= ${:directory}/src