Log Message:
Update go112 to 1.12.7.

This fixes a nasty code-generation bug, among other things:

go1.12.6 (released 2019/06/11) includes fixes to the compiler, the linker,
the go command, and the crypto/x509, net/http, and os packages.
See the Go 1.12.6 milestone on our issue tracker for details.

go1.12.7 (released 2019/07/08) includes fixes to cgo, the compiler,
and the linker. See the Go 1.12.7 milestone on our issue tracker for details.