re PR go/88927 (Bootstrap failure on arm in libgo starting with r268084)

re PR go/88927 (Bootstrap failure on arm in libgo starting with r268084)

	PR go/88927
    runtime, internal/cpu: fix build for ARM GNU/Linux

    Was failing with

    ../../../libgo/go/internal/cpu/cpu.go:138:2: error: reference to undefined name 'doinit'
      138 |  doinit()
          |  ^

    Fix it by adding in Go 1.12 internal/cpu/cpu_arm.go, and the code in
    runtime that initializes the values.

    Fixes https://gcc.gnu.org/PR88927.

    Reviewed-on: https://go-review.googlesource.com/c/158717

From-SVN: r268131