This patch to the Go frontend exports the type "any" as a builtin.
Otherwise we can't tell the difference between builtin type "any" and
a locally defined type "any".

This will require updates to the gccgo export data parsers in the main
Go repo and the x/tools repo.  These updates are https://go.dev/cl/537195
and https://go.dev/cl/537215.

Bootstrapped and ran Go testsuite on x86_64-pc-linux-gnu.  Committed
to mainline.

Ian