golang: v<E2><86><91> to go1.12

Do not change any defaults regarding 1.9, 1.10 and 1.11.

component/golang/buildout.cfg

@@ -58,6 +58,15 @@ environment-extra =
 url = https://dl.google.com/go/go1.11.4.src.tar.gz
 md5sum = a77697673215be465d1b583680ef2318
 
+# go1.11 needs go1.4 to bootstrap
+environment-extra =
+  GOROOT_BOOTSTRAP=${golang14:location}
+
+[golang1.12]
+<= golang-common
+url = https://dl.google.com/go/go1.12.src.tar.gz
+md5sum = b3332feba8a945a193b47a52d9981bb9
+
 # go1.11 needs go1.4 to bootstrap
 environment-extra =
   GOROOT_BOOTSTRAP=${golang14:location}