Log Message:
Update go115 to 1.15.12.

go1.15.11 (released 2021/04/01) includes fixes to cgo, the compiler, linker,
runtime, the go command, and the database/sql and net/http packages. See the Go
1.15.11 milestone on our issue tracker for details.

go1.15.12 (released 2021/05/06) includes a security fix to the net/http
package, as well as bug fixes to the runtime and the time package. See the Go
1.15.12 milestone on our issue tracker for details.